The US military said it had new information one of Saddam Hussein's most feared lieutenants was involved in some of the attacks that have killed at least 177 US soldiers since the official end of major combat in Iraq on May 1.

US troops have responded to an escalation in the insurgency against them by deploying in the anti-American heartlands to the north and west of Baghdad heavy and high-tech weaponry rarely used since Saddam's ouster in April.

Faced with growing criticism at home of the invasion and occupation, Bush was due to lean on his closest ally, British Prime Minister Tony Blair, on a state visit to London.

In Brussels, Secretary of State Colin Powell was expected to woo more skeptical members of the European Union.

Neither faced an easy task. Several EU states, led by France and Germany, were resolutely opposed to the war as was much of the British public. Up to 100,000 people are expected to gather in London to protest against Bush and his policies.

Underlining the gravity of the security situation in Iraq, UN Secretary General Kofi Annan left open an early return of political staff. He said they might operate outside the country.

But he did pledge to name a replacement soon for his special representative Sergio Vieira de Mello, who was among 22 people killed when their Iraq headquarters was bombed on August 19.

In Baquba, some 60km north of Baghdad, two F-15 fighter jets flew from the Gulf state of Qatar to drop four 500-pound bombs on farmhouses and other sites suspected to have been used by guerrillas.

"We had taken action on these targets before, but this is to demonstrate one more time that we have significant firepower and we can use it at our discretion," said ground commander Lieutenant-Colonel Mark Young of the 4th Infantry Division.