Asked how the battle was going, Commander Abu Mohammad Hilu showed off his latest trophy - a blood-drenched American boot. There was a large bullet hole in the middle. "We found it after last night's battle," the commander explained. His colleague, Abu Ali, added: "Originally there was an American foot inside it and a bit of the leg. But we took it out and threw it to the dogs." But the most tangible evidence of the Mahdi army's extraordinary self-confidence yesterday, however, came too close for comfort half an hour earlier. We had been driving through the high street in Kufa, another stronghold of the Shia cleric Muqtada Sadr, some three kilometres from the shrine where he and his supporters are still holed up.
We stopped to inspect a building - this was a mistake. Mahdi army soldiers armed with Kalashnikovs spotted us, then targeted us. In a convoy of two cars, with guns pointing and pushing at us, we were taken to Kufa's mosque.
Ten minutes later The Observer's Iraqi fixer got us released after phoning a high-ranking Sadr aide.
The aggression disappeared, the fighters turned profusely apologetic. More than two weeks after launching their uprising in Najaf, the Mahdi army was - despite reports to the contrary - still in control of Najaf's Imam Ali shrine - and much of the rest of Iraq. Yesterday fighting carried on.
In pre-dawn darkness, American tanks and Humvees also staged a raid on Kufa, trundling down the high street and past the library. Commander Hilu and his men were waiting.
"The Americans went as far as the mosque then got out," the commander said, having escorted me back to the scene of what, he suggested, was a heroic victory.
"It was an ambush. All of a sudden we started shooting them. They were surprised. We destroyed two of their tanks."
Hilu showed off the newly incinerated Kufa court building just across the road. Here, he said, US troops had taken refuge under fire. Crunching over the melted remains of ceiling fans, he pointed to a small annexe room soaked in blood.
"They treated their wounded in here. They were firing in the air at the same time. That's a piece of American brain," he added helpfully. "We found the boot nearby."
Over the past 17 days the standoff between Sadr's Shia militia and Iraq's US-backed interim government has been portrayed as a conflict that the renegade cleric will eventually lose. In fact, he is winning.
On Friday afternoon Iraq's interior minister claimed his police had taken control of Najaf's Imam Ali shrine and arrested several hundred "lightly armed" fighters.
It was a boast that might have come from Saddam Hussein's notoriously unreliable information minister, "Comical Ali".
Arriving at the mosque a couple of hours later, I found nothing had changed. Hundreds of unarmed supporters of Sadr still loafed on mats inside the shrine's courtyard.
In the narrow alleyways around the mosque, Mahdi army fighters - one wearing a black Manchester United strip - chatted in the late afternoon sunshine.
Yesterday Sheikh Azhar Kenani, head of Kufa mosque, told The Observer that his fighters would mow down Iraqi troops, should they attempt to storm the shrine.
"One hundred per cent there will be a massacre," the sheikh predicted. "The Iraqi police are agents of the Americans. We will not allow the US's agents or the Americans themselves to occupy this holy site."
Sadr's uncompromising rejection of foreign occupation does not resonate with all Iraqis, but has the virtue of intellectual consistency.
"The interim government is illegitimate and doesn't represent the Iraqi nation. Therefore we reject it," the sheikh said.
He added: "We demand that all occupying forces leave our country." Who did he think would win the battle for Najaf? "We will. The Americans are fighting because of money. But we are fighting by the power of God."
The sheikh said that his colleagues inside Najaf's shrine were trying to hand over the mosque's keys to representatives of Grand Ayatollah Ali Sistani - Iraq's most revered Shia cleric.
But he has been reluctant to embroil himself in the crisis and is currently receiving heart treatment in London. The gesture is unlikely to end the standoff, the sheikh admitted.
Sitting cross-legged on a carpet outside Kufa's gold-domed mosque, over cups of sweet black tea, other Mahdi army fighters yesterday said they had no intention of giving up.
Nearby, a group of men were carrying away the latest martyr for burial - killed at 3am yesterday when an American tank blew a hole through the west corner of the neighbouring Maitham Tamar mosque.
"I lost three fingers while fighting in the cemetery last week," Abu Muqtada, 38, explained, waving his bandaged right hand. "An American helicopter shot me from the sky. But my other hand is still working. I can fight with that."
Muqtada admitted that many of his comrades had been killed in the cemetery, the vast rambling area to the north of Najaf's old city, where intense fighting took place last week. "We take away all our dead friends," he pointed out. "We clean them up and give them a proper burial."
Inside the blue-painted police station on the edge of Najaf, meanwhile, there is little appetite for an apocalyptic final battle with the Mahdi army.
But even if American forces do seize the shrine, it seems unlikely that the Sadr insurgency raging across Shia Iraq will disappear.
In Kufa, there are no Americans to be seen. There is, however, plenty of damage. The College of Economics, which overlooks the shimmering Euphrates river, had a large Edam-shaped hole gouged out of its roof by an American bomb early yesterday.
US warplanes control the skies above Kufa, dropping two bombs at 7am yesterday on a deserted mosque. But they don't control its streets - or the densely packed alleys around Najaf's shrine, where the Mahdi army appears to have shrugged off nights of bombardment. "It was a big battle. They came at us from four directions," Hilu said.
"None of the soldiers in my unit were injured." He added: "You will write about the boot, won't you?"