The US military says it has launched its biggest air offensive in Iraq since the 2003 invasion of the country.
A military statement said the operation was targeted at suspected insurgents operating in an area near the town of Samarra, over 125km north of Baghdad.
Samarra was the site of a bomb attack last month on a Shia shrine that sparked sectarian violence in which hundreds of people were killed.
The operation involved more than 50 aircraft, 1,500 Iraqi and US troops and 200 tactical vehicles.
Bomb lands close to convention centre
In a separate development, a mortar bomb landed 100 metres away from the convention centre in Baghdad's heavily-fortified Green Zone, hours after the country's new parliament had convened there for its first time.
Witnesses said parliamentarians had left the building before the explosion. There were no reports of casualties.
The parliament met three months after the general election, with no sign of agreement on the formation of the new government.
With sectarian violence on the increase, the formation of a government of national unity is seen as essential.
The United States has been exerting pressure on Iraqi leaders to do it as soon as possible.
However with no agreement among Shias, Sunnis and Kurds on the posts of speaker, president, prime minister or cabinet members, no substantive business could be conducted today.
The short session was held against a backdrop of increasing sectarian violence and predictions of civil war.
The parliament is dominated by the Shia United Iraqi Alliance, which can count on the support of 130 MPs. The Kurdish coalition has 53 seats, while various Sunni parties control at least 55 seats.
Teenager killed in Halabja riot
Meanwhile, a 14-year-old boy has been killed and six demonstrators injured after Iraqi security forces fired into a crowd of several thousand Kurds rioters in the town of Halabja.
The violence flared on the anniversary of Saddam Hussein's gas attack on the Kurdish town in 1988.
At least 7,000 demonstrators, including relatives of the 5,000 victims of the gas attack, set up road blocks, attacked government offices and set fire to a memorial built to honour the dead.
