Operation Swarmer, involving more than 1,500 Iraqi and coalition troops and 50 aircraft, mainly helicopters, came as the new parliament was sworn in to give momentum to protracted talks on the formation of a new government.
The operation aims to clear a suspected insurgent operating area north-east of Samarra, over 125 kilometres north of Baghdad.
US forces recently said a number of al Qaeda insurgents were ensconced in the hilly area, known as Hamreen. "Initial reports from the objective area indicate that a number of enemy weapons caches have been captured," a statement said, adding that the operation could continue for several days.
With inter-communal tensions still rife in Iraq the country's first full-term parliament since the ouster of Saddam Hussein in April 2003 opened on Thursday.
But continuing deadlock on choosing a prime minister, a president and a parliamentary speaker led to the chamber calling it a day after 20 minutes.
Officially, the session, held deep inside Baghdad's fortified Green Zone protected by walls, razor wire and troops, remains open until such a time as a speaker and his deputies are elected by the new 275-strong assembly.
"It has been decided to leave the session open pending political agreement on the designation of a speaker and his two deputies," said Adnan Pachachi, 83, who presided as eldest member. Outgoing speaker Hajem al-Hassani said, "it is difficult to chose a new speaker and his deputies until a deal is reached on the whole government package." The summoning of parliament, dominated by the Shia United Iraqi Alliance (UIA), was meant to provide new momentum to talks between Shia, Sunni and Kurdish factions on forming a coalition at a time of worsening sectarian violence which threatens to trigger civil war.
The latest sign of such bloodletting came with authorities announcing the discovery on Thursday of 25 corpses - men who had been shot dead and dumped in different parts of the capital. At least 80 more were found earlier in the week.
The streets of the capital had remained eerily quiet with traffic barred to keep car bombers at bay, while police and army units multiplied their checkpoints across the city.
The government told civil servants to take a holiday and many other residents bunkered down at home, fearing attacks by insurgents, bent on proving the caretaker government cannot guarantee security. Most shops remained closed.
The UIA can count on the support of 130 MPs, while the Kurdish coalition has 53 seats and various Sunni parties control at least 55 seats. Secular-based and minority parties hold the remainder.
All factions, egged on by US authorities, have called for the formation of a government of national unity, but have so far failed to even agree on who would lead the next cabinet.
Outgoing Prime Minister Ibrahim Jaafari suggested that forming the cabinet might take only another month.
"If we stick to the Constitution, it shouldn't take much more than a month," he told reporters. "But of course if one tries to go outside the constitution to set up new executive bodies, then that will take much longer."