"President" Hosni Mubarak's counter-revolution smashed into his opponents yesterday in a barrage of stones, cudgels, iron bars and clubs, an all-day battle in the very centre of the capital he claims to rule between tens of thousands of young men, both – and here lies the most dangerous of all weapons – brandishing in each other's faces the banner of Egypt. It was vicious and ruthless and bloody and well planned, a final vindication of all Mubarak's critics and a shameful indictment of the Obamas and Clintons who failed to denounce this faithful ally of America and Israel.

The fighting around me in the square called Tahrir was so terrible that we could smell the blood. The men and women who are demanding the end of Mubarak's 30-year dictatorship – and I saw young women in scarves and long skirts on their knees, breaking up the paving stones as rocks fell around them – fought back with an immense courage which later turned into a kind of terrible cruelty.

Some dragged Mubarak's security men across the square, beating them until blood broke from their heads and splashed down their clothes. The Egyptian Third Army, famous in legend and song for crossing the Suez Canal in 1973, couldn't – or wouldn't – even cross Tahrir Square to help the wounded.

As thousands of Egyptians shrieking abuse – and this was as close to civil war as Egypt has ever come – swarmed towards each other like Roman fighters, they simply overwhelmed the parachute units "guarding" the square, climbing over their tanks and armoured vehicles and then using them for cover.

One Abrams tank commander – and I was only 20 feet away – simply ducked the stones that were bouncing off his tank, jumped into the turret and battened down the hatch. Mubarak's protesters then climbed on top to throw more rocks at their young and crazed antagonists.

I guess it's the same in all battles, even though guns have not (yet) appeared; abuse by both sides provoked a shower of rocks from Mubarak's men – yes, they did start it – and then the protesters who seized the square to demand the old man's overthrow began breaking stones to hurl them back. By the end of the day there were reports of three deaths in Cairo, and widespread accounts that the pro-Mubarak crowds were deliberately targeting Western journalists.

By the time I reached the "front" line – the quotation marks are essential, since the lines of men moved back and forth over half a mile – both sides were screaming and lunging at each other, blood streaming down their faces. At one point, before the shock of the attack wore off, Mubarak's supporters almost crossed the entire square in front of the monstrous Mugamma building – relic of Nasserite endeavour – before being driven out.

Indeed, now that Egyptians are fighting Egyptians, what are we supposed to call these dangerously furious people? The Mubarakites? The "protesters" or – more ominously – the "resistance"? For that is what the men and women struggling to unseat Mubarak are now calling themselves.

"This is Mubarak's work," one wounded stone-thrower said to me. "He has managed to turn Egyptian against Egyptian for just nine more months of power. He is mad. Are you in the West mad, too?" I can't remember how I replied to this question. But how could I forget watching – just a few hours earlier – as the Middle East "expert" Mitt Romney, former governor of Massachusetts, was asked if Mubarak was a dictator. No, he said, he was "a monarch-type figure".

The face of this monarch was carried on giant posters, a printed provocation, to the barricades. Newly distributed by officers of the National Democratic Party – they must have taken a while to produce after the party's headquarters was reduced to a smouldering shell after Friday's battles – many were held in the air by men carrying cudgels and police batons. There is no doubt about this because I had driven into Cairo from the desert as they formed up outside the foreign ministry and the state radio building on the east bank of the Nile. There were loudspeaker songs and calls for Mubarak's eternal life (a very long presidency indeed) and many were sitting on brand-new motorcycles, as if they had been inspired by Mahmoud Ahmadinejad's thugs after the 2009 Iranian elections. Come to think of it, Mubarak and Ahmadinejad do actually have the same respect for elections.

Only when I had passed the radio building did I see the thousands of other young men pouring in from the suburbs of Cairo. There were women, too, mostly in traditional black dress and white-and-black scarves, a few children among them, walking along the flyover behind the Egyptian Museum. They told me that they had as much right to Tahrir Square as the protesters – true, by the way – and that they intended to express their love of their President in the very place where he had been so desecrated.

And they had a point, I suppose. The democrats – or the "resistance", depending on your point of view – had driven out the security police thugs from this very square on Friday. The problem is that the Mubarak men included some of the very same thugs I saw then, when they were working with armed security police to baton and assault the demonstrators. One of them, a yellow-shirted youth with tousled hair and bright red eyes – I don't know what he was on – carried the very same wicked steel stick he had been using on Friday. Once more, the defenders of Mubarak were back. They even sang the same old refrain – constantly reworked to take account of the local dictator's name – "With our blood, with our soul, we dedicate ourselves to you."

As far away as Giza, the NDP had rounded up the men who controlled voting at elections and sent them hollering their support as they marched along a stinking drainage ditch. Not far away, even a camel-owner was enjoined to say that "if you don't know Mubarak, you don't know Allah" – which was, to put it mildly, a bit much.

In Cairo, I walked beside Mubarak's ranks and reached the front as they began another charge into Tahrir Square. The sky was filled with rocks – I am talking of stones six inches in diameter, which hit the ground like mortar shells. On this side of the "line", of course, they were coming from Mubarak's opponents. They cracked and split apart and spat against the walls around us. At which point, the NDP men turned and ran in panic as the President's opponents surged forward. I just stood with my back against the window of a closed travel agency – I do remember a poster for a romantic weekend in Luxor and "the fabled valley of the tombs".

But the stones came in flocks, hundreds of them at a time, and then a new group of young men were beside me, the Egyptian demonstrators from the square. Only no longer in their fury were they shouting "Down with Mubarak" and "Black Mubarak" but Allahu Akbar – God is Great – and I would hear this again and again as the long day progressed. One side was shouting Mubarak, the other God. It hadn't been like that 24 hours ago.

I hared towards safe ground where the stones no longer hissed and splintered and suddenly I was among Mubarak's opponents.

Of course, it would be an exaggeration to say that stones cloaked the sky, but at times there were a hundred rocks soaring through the sky. They wrecked an entire army truck, smashing its sides, crushing its windows. The stones came out of side roads off Champollion Street and on Talaat Harb. The men were sweating, headbands in red, roaring their hatred. Many held white cloth to wounds. Some were carried past me, sloshing blood all over the road.

And an increasing number were wearing Islamist dress, short trousers, grey cloaks, long beards, white head caps. They shouted Allahu Akbar loudest and they bellowed their love of God, which was not supposed to be what this was all about. Yes, Mubarak had done it. He had brought the Salafists out against him, alongside his political enemies. From time to time, young men were grabbed, their faces fist-pulped, screaming and fearful of their lives, documentation found on their clothes to prove they worked for Mubarak's interior ministry.

Many of the protesters – secular young men, pushing their way through the attackers – tried to defend the prisoners. Others – and I noticed an awful lot of "Islamists" among them, complete with obligatory beards – would bang their fists on these poor men's heads, using big rings on their fingers to cut open their skin so that blood ran down their faces. One youth, red T-shirt torn open, face bloated with pain, was rescued by two massive men, one of whom put the now half-naked prisoner over his shoulder and pushed his way through the crowd.

Thus was saved the life of Mohamed Abdul Azim Mabrouk Eid, police security number 2101074 from the Giza governorate – his security pass was blue with three odd-looking pyramids stamped on the laminated cover. Thus was another man pulled from the mob, squealing and clutching his stomach. And behind him knelt a squadron of women, breaking stones.

There were moments of farce amid all this. In the middle of the afternoon, four horses were ridden into the square by Mubarak's supporters, along with a camel – yes, a real-life camel that must have been trucked in from the real dead pyramids – their apparently drugged riders hauled off their backs. I found the horses grazing gently beside a tree three hours later. Near the statue of Talaat Harb, a boy sold agwa – a peculiarly Egyptian date-bread delicacy – at 4 pence each – while on the other side of the road, two figures stood, a girl and a boy, holding identical cardboard trays in front of them. The girl's tray was filled with cigarette packets. The boy's tray was filled with stones.

And there were scenes that must have meant personal sorrow and anguish for those who experienced them. There was a tall, muscular man, wounded in the face by a slice of stone, whose legs simply buckled beside a telephone junction box, his face sliced open yet again on the metal. And there was the soldier on an armoured personnel carrier who let the stones of both sides fly past him until he jumped on to the road among Mubarak's enemies, putting his arms around them, tears coursing down his face.

And where, amid all this hatred and bloodshed, was the West? Reporting this shame every day, you suffer from insomnia. Sometime around 3am yesterday, I had watched Lord Blair of Isfahan as he struggled to explain to CNN the need to "partner the process of change" in the Middle East. We had to avoid the "anarchy" of the "most extreme elements". And – my favourite, this – Lord Blair spoke of "a government that is not elected according to the system of democracy that we would espouse". Well, we all know which old man's "democracy" he was referring to.

Street rumour had it that this man – Mitt Romney's "monarch-type figure" – might creep out of Egypt on Friday. I'm not so sure. Nor do I really know who won the Battle of Tahrir Square yesterday, though it will not remain long unresolved. At dusk, the stones were still cracking on to roads, and on to people. After a while, I started ducking when I saw passing birds.

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