U.S. launches major new offensive in Iraq

BAGHDAD (Reuters) - U.S. forces launched a big offensive in Iraq with an airborne assault targeting al Qaeda guerrillas on Tuesday, part of a major new countrywide push.

The Americans also raided Baghdad's Shi'ite slum of Sadr City targeting militants they said are linked to Iran. Relatives said a 5-year-old girl was among four killed in the raid.

Suicide bombers driving fuel tankers killed 20 people in an apparent attack on an ancient minority sect in northern Iraq, police said. In a separate attack, a suicide truck bomber killed 10 people and destroyed a bridge linking Baghdad to the north.

Five U.S. service personnel were killed when a military transport helicopter crashed during a routine flight west of Baghdad, the U.S. military said.

The military said 16,000 U.S. and Iraqi troops were involved in Operation Lightning Hammer against Sunni Islamist al Qaeda in the fertile area of the Diyala River north of Baghdad.

U.S. and Iraqi soldiers started the operation with an air assault, focusing on militants who fled an earlier crackdown in the provincial capital Baquba.

"Our main goal with Lightning Hammer is to eliminate the terrorist organizations ... and show them that they truly have no safe haven, especially in Diyala," Major-General Benjamin Mixon, U.S. commander in northern Iraq, said in a statement.

The operation was described as part of the larger countrywide Operation Phantom Strike, which U.S. forces announced on Monday.

Al Qaeda is widely seen as trying to influence debate in Washington by stepping up attacks in Iraq before a crucial progress report on the war is delivered to Congress on September 15.

Pentagon spokesman Bryan Whitman said U.S. forces would launch a series of operations over the next 30 days.

"We fully expect that al Qaeda in Iraq would like to increase their attacks during this critical period," he told reporters in Washington.

WORST VIOLENCE

U.S. military offensives have been under way in Baghdad in the past few months and surrounding provinces like Diyala, a sectarian patchwork, have seen some of Iraq's worst violence.

Police in the Diyala town of Khalis said they found 15 corpses identified as Sunni Arabs, executed by gun shots and dumped on the highway linking Baghdad and Kirkuk.

Police and an oil industry source said gunmen had kidnapped a senior official of Iraq's state oil marketing organization, although details of the incident were sketchy.

The United States has sent an additional 30,000 troops to Iraq this year and moved them from large bases into small neighborhood outposts in an effort to reduce sectarian violence in the capital and surrounding provinces.

U.S. forces say they have had success, especially against Sunni Arab militants who were their main enemies for the first three years after the fall of President Saddam Hussein in 2003.

But they have also faced violence from Shi'ite militiamen, who they say have ties to neighboring Shi'ite Muslim Iran.

Imam Ali Hospital in Sadr City said it had received three bodies, including a 5-year-old girl and her father, shot dead during the U.S. raid in the Shi'ite stronghold. Angry mourners marched through the slum with flag-draped coffins.

Blood stained the mattress where the family said the girl was killed as they slept on the roof of the house to keep cool.

U.S. military spokesman Lieutenant Colonel Christopher Garver said troops fired only "at people who fired at them". The raid was meant to capture a militant leader using materials smuggled from Iran to carry out killings, U.S. forces said.

Washington says one aim of its military push this year is to provide a window for Iraqi politicians to agree on steps to end sectarian violence, but U.S. officials have complained about the slow pace of Iraqi political efforts.

The political crisis worsened this month when the main Sunni Arab bloc pulled out of the national unity government.

Three members of a secularist political bloc that had also been part of the boycott attended a cabinet session on Tuesday.

Prime Minister Nuri al-Maliki has summoned the leaders of Iraq's main political factions for a summit to resolve their differences, expected to begin in days.

(Additional reporting by Ahmed Rasheed, Aseel Kami and Mariam Karouny in Baghdad)