BAGHDAD - US forces launched a big offensive in Iraq's Diyala province on Tuesday as part of a major new countrywide push against Sunni and Shi'ite militants announced this week.
The military said 16,000 US and Iraqi troops were involved in Operation Lightning Hammer against Sunni Arab al Qaeda militants in Diyala province, the fertile crescent of the Diyala River which flows from the north into the Tigris near Baghdad.
US and Iraqi soldiers initiated the operation with a late-night air assault, they said. The operation's focus is to target militants who fled an earlier crackdown in the provincial capital Baquba into the river valley north of the city.
"Al Qaeda cells were disrupted and forced into hiding ... in June and July," Major-General Benjamin Mixon, commander of US troops north of Baghdad, said in a statement. "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."
The operation was described as part of a larger countrywide Operation Phantom Strike, which US forces announced on Monday.
They have so far given few details of Phantom Strike. But US military offensives over recent months have been under way in the Tigris and Diyala valleys north of Baghdad and in the Euphrates valley south of the capital.
The United States has sent an additional 30,000 troops to Iraq this year and moved them from large bases into small bases in neighborhoods in an effort to reduce sectarian violence in the capital and the surrounding provinces.
US 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 faced increasing violence from Shi'ite militia, who they say have ties to Iraq's Shi'ite Muslim neighbor Iran.
The military said it raided Baghdad's Sadr City Shi'ite slum on Sunday, killing up to five militants and arresting 13 believed to be involved in bringing armor-piercing bombs from Iran. Last week US forces said they had killed an estimated 30 militants in an air strike during a raid in the area.
Washington says one of the aims of its military push this year is to provide a window for Iraqi politicians to agree on steps to end sectarian violence, but US 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. Other groups are also boycotting, and nearly half of the cabinet is no longer participating in cabinet meetings.
Prime Minister Nuri al-Maliki said on Sunday he had summoned the leaders of Iraq's main political factions for a summit to resolve their differences. He said it would begin in the next two days although so far it has not materialized.
The leaders have been holding a series of bilateral talks, seeking to find common ground in preparation for the summit.