Washington: As US forces are drawn further into renewed fighting, the potential for deepening chaos in Iraq is raising questions whether the Bush administration made a wise decision or a costly miscalculation by backing a government offensive against Shiite militias.

President Bush said on Friday that the offensive answered critics who have accused Prime Minister Nouri Al Maliki's Shiite-dominated government of inaction and of favouritism toward Shiites.

"I would say this is a defining moment in the history of a free Iraq," Bush said at the White House.

"The decision to move troops, Iraqi troops, into Basra talks about Prime Minister Al Maliki's leadership."

But some of the administration's allies have begun to question the timing and wisdom of the offensive, which appeared to be meeting stiff resistance since it was launched on Tuesday in the southern city of Basra. Since then, fighting against Shiite militiamen has spread through much of southern Iraq and into Baghdad. Iraqi forces have called in US air strikes to fend off well-armed groups in Basra, including an attack by a Navy jet on a mortar position.

Signifying the potential difficulty ahead, other US assets, including special operations forces and spy planes, are expected to join the fight as well.

Wrong time

Within the Pentagon, officers expressed concern about the rapid spillover of violence into areas where US forces have spent more than a year working to restore order, especially the Shiite neighbourhoods of Baghdad.

US officials have long believed that Iraqi militias should be disbanded. But military analysts inside and outside the Pentagon are questioning whether this was the time and the place to do it.

The offensive comes two weeks before Army Gen David H. Petraeus testifies on his plans for Iraq. Petraeus is known for opening his recent presentations by displaying what aides call his favourite slide: a chart showing attacks in Iraq spiking last summer but dramatically dropping after the introduction of 28,500 extra troops. Pentagon officials worry that the recent violence would mar that otherwise compelling narrative.

The extra troops are scheduled to leave by the end of July, and Petraeus is expected to make a recommendation on whether and how fast US troops should be sent home after that.

As violence has spread over the past week, the relative calm that had been returning to Baghdad was disrupted by images that recalled the sectarian war pre-dating the US troop buildup: repeated shelling of the fortified Green Zone; outraged street demonstrations by Shiite protesters; checkpoints in the slums of Sadr City manned by Mahdi Army militiamen loyal to cleric Moqtada Al Sadr.

The US Embassy was locked down and Baghdad is under a curfew.

In his White House appearance on Friday with Kevin Rudd, the new Australian prime minister, Bush seemed unsure about the timing of the offensive, saying he had yet to talk to Al Maliki about it.

Bush said the offensive showed the newfound capability of the Iraqi armed forces and resolve of the country's leaders, especially Al Maliki. But Al Maliki, who travelled to Basra to oversee the operation, faces a heavy political cost if it bogs down, and already is confronting demands for his resignation.

Bush said on Friday the four-day-old offensive was launched by Al Maliki to confront those outside the law, explaining that Basra is an Iraqi "port" with goods and services that has drawn criminals.

"This is a test and a moment for the Iraqi government," Bush said. "And it is an interesting moment for the people of Iraq because ... they must have confidence in their government's ability to protect them and to be even-handed."

But retired Army General Jack Keane, an architect of last year's US troop buildup, suggested on Friday that Al Maliki acted out of personal animus toward Al Sadr, rather than the best interest of Iraq.

"He's a very impulsive person," Keane said of Al Maliki in a National Public Radio interview. "I think that's what happened here. I think he's way out in front of what the military realities on the ground are."

Gary J. Schmitt, a military analyst at the American Enterprise Institute who was an early supporter of the troop buildup, said he believed the Bush administration was taken by surprise by Al Maliki's decision, but that with provincial elections set for October, the central government had to act.

"Tactically, this might not have been the optimal moment, or they may not have prepared as well as they should have. But I think it was quite predictable," Schmitt said. "With the elections coming, it should have been understood as a necessity."

The timing also could affect the US presidential election campaign. A spike in violence would hinder the ability of Republican Sen John McCain of Arizona, an early supporter of the troop increase, to campaign on the success of the strategy. It also would trip up Bush's hopes to leave office with Iraq appearing to be on a glide path to stability.

Support: UK battles pressure

British forces were facing increasing pressure to intervene in fighting in southern Iraq on Friday after government efforts to defeat Shiite militias in Basra ground to a halt.

Signs of a rift were growing among British officials as diplomats said that UK forces "stand ready to support" Iraqi soldiers as and when requested. This contradicted military statements that British forces would be confined to "niche" roles.

The Iraqi Government's lack of success in Basra was highlighted when Prime Minister Nouri Al Maliki extended a deadline by 10 days for Shiite militia loyal to the cleric Moqtada Al Sadr to give up their weapons in exchange for cash.

For the first time since violence broke out on Tuesday, US and British warplanes carried out bombing raids in Basra, and one Iraqi official conceded that coalition ground support was needed. While a British Army spokesman ruled out intervention on the ground, diplomats in the Baghdad embassy lobbied for a signal from Britain that troops could be deployed.

- The Telegraph Group Limited, London 2008