Launching a new strategy to rescue Iraq from civil war, Washington told the government of Prime Minister Nuri Al Maliki, who owes his job to Sadr, it was on "borrowed time" and declared new "no holds barred" military operations.

A cornerstone of the new approach is increased pressure on Iraq's neighbors Iran and Syria - which are accused by Washington of fomenting unrest - and tougher action to deal with militias such as Sadr's feared Mehdi Army.

"The American people have to prevent their sons from coming to Iraq or they may return in coffins," threatened Sheikh Abdel Razzaq Al Nadawi, a senior official in Sadr's movement, slamming the planned US troop increase.

His threat compounded tensions over the detention of five Iranians in a US swoop on an official building earmarked as a consulate in Arbil, the capital of Iraqi Kurdistan, which Tehran branded a breach of international law.

Sheikh Jaber Al Khafaji, another close Sadr aide, also slammed the new US strategy during his Friday sermon in the Shiite holy city of Kufa.

"The Sadr movement rejects the new mundane policies. Their new strategy targets the faithful and believers who rejected the occupation, injustice, and bondage," he told worshipers.

The glowering cleric Sadr is one of the fiercest opponents of the US presence in Iraq and his Mehdi Army has been branded by the Pentagon as the most dangerous faction in Iraq's bloody sectarian war.

It is just one of many militias alleged to have received arms from Iran. On Thursday, US troops swooped on an Iranian consular office in Arbil and seized six staff, along with computers and office records.

Iraqi foreign minister Hoshyar Zebari said that the five detainees - one was released overnight - had been working with Iraqi government sanction but their Arbil office had not yet become a full consulate.

"It is a liaison office. There was a request to change it into consulate," he said, adding that the office had been working for 10 years. "We had already agreed with the Iranians to open consulates in Arbil and Sulaimaniyah in return for opening [Iraqi] consulates in [Iranian cities] Mashhad and Ahwaz. These procedures have not been finalized," he said.

Witnesses said that soldiers dropped around the building, just 100 meters (yards) from the Kurdistan administration in downtown Arbil, from helicopters and two Humvees and threw stun grenades in a show of force.

There were no clashes with Kurdish security guards but US grenades shattered windows in the two-storey building and troops ordered all those inside to surrender before lowering the Iranian flag and abandoning the premises.

Fuad Hussein, a senior official in the Kurdish presidency, said that the regional government, one of the staunchest US allies in the Middle East, was not given advance warning about the operation.

Thursday's raid came after President George W. Bush warned that the United States would not tolerate Iranian meddling in Iraq, where US commanders believe that Tehran's agents have been arming militias and inciting anti-American attacks.

A US defense official confirmed that six Iranians were arrested.

"The president made it clear last night that we will not tolerate outside interference in Iraq. And that's what the Iranians are up to," said national security spokesman Gordon Johndroe.

Bush has ordered 21,500 more troops to Iraq and promised to take aggressive steps to curtail what he described as Iranian and Syrian help for insurgents.

Secretary of State Condoleezza Rice, who Friday leaves to sell the US plan to allies in the Middle East, vowed that the United States would not let Tehran disrupt Washington's plan to stabilize Iraq.

US Defense Secretary Robert Gates also warned that all Baghdad districts would be now targeted under the new American strategy with Iraqi approval, including the Sadr City slum area, Sadr's stronghold in Baghdad.

Further stepping up its military presence in the region, Washington plans to keep two aircraft carrier battle groups in the Gulf for the first time since the 2003 invasion of Iraq.