Saleh Mutlak said: "This large operation that used airplanes is sending a signal to parliament and Iraqis that the solution is military and not political."

The offensive comes at a time when Zalmay Khalilzad, the US ambassador to Iraq, has been mediating to narrow differences among Iraqi politicians still struggling to form a government three months after parliamentary polls.

The US military said that 50 people had been detained and 30 remained in custody as a result of "Operation Swarmer", which began on Thursday, would last several days.

The Pentagon released video footage to news organisations of soldiers being flown in helicopters to landing zones northeast of Samarra, 100km north of Baghdad, where the bombing of a Shia shrine last month prompted fears of civil war.

Overreaction

An Iraqi defence ministry spokesman criticised the attention being given to the assault, describing it as one of many operations aimed at rooting out rebels and seizing weapons.

"This large operation that used airplanes is sending a signal to parliament and Iraqis that the solution is military and not political"

Saleh Mutlak, Iraqi politician

Salih Sarhan said: "This operation is not an invasion and the media have overreacted. The operation aims to search and control the area and launch raids against some suspected places."

Iraqis were sceptical about the assault. Alaa, a resident of Baghdad, said: "We often hear about these offensives but frankly I really don't see what their purpose is."

The raids, carried out jointly by US and Iraqi troops, on suspected strongholds of armed groups came as Iraq's political leadership prepared to meet again in an effort to break a deadlock on forming a unity government that might avert civil war.