March 28 (Bloomberg) -- U.S. aircraft bombed militia positions in Basra overnight, joining the four-day fight between Iraqi forces and Shiite Muslim cleric Moqtada al-Sadr's Mahdi Army in the southern oil hub.

U.S. aircraft bombed ``positively identified militia targets,'' including ``groups of militia that were targeting Iraqi forces,'' Major Tom Holloway, a spokesman for U.K. forces based on the outskirts of Basra, said today by telephone. ``The support was requested by Iraqi forces.''

Handing over the security of Iraq to Iraqi forces is a key policy of the U.S.-led coalition, and the U.S. today made it clear plans for reducing the number of U.S. troops in Iraq would go ahead. The U.K. transferred the southern, oil-rich province of Basra to Iraqi forces in December. Half of Iraq is now under Iraqi provincial control and the government has said it hopes to take over the remaining provinces as soon as possible.

U.S. President George W. Bush said today that the Iraqi government's decision to combat militants in Basra marks ``a defining moment'' in the country's history.

``It's an issue for all of Iraq,'' not just Prime Minister Nuri al-Maliki, Iraq government spokesman Ali al-Dabbagh said in a telephone interview from Baghdad. ``Basra is very important for Iraq. In other places some people tried, smaller groups, to create problems for the security forces. There's no choice for the government, it has to impose the rule of law.''

April Deadline

Al-Maliki announced a deadline of April 8 today for the militia groups to hand over medium and heavy weapons in Basra in exchange for money, according to a statement read out on state television. A separate, original 72-hour deadline for an end to the fighting and due to expire tomorrow is still in place. The parliament held an emergency meeting on how to resolve the crisis, state television said.

Crime and violence have ensued in Basra for two years and it's not acceptable, al-Dabbagh said. ``In Basra, the government is confronting the gangs, the smugglers and there is no way the government will stop this'' operation.

The strikes were the first bombing missions by the coalition to back Iraqi army and police forces that have fought running battles against gunmen in an operation that began early on March 25. Fighting in Basra, Baghdad, and Kut involving Iraqi and U.S. forces and Shiite groups has claimed at least 100 lives this week. Two guards were killed when mortar shells hit an Iraqi vice presidential office in Baghdad, the Associated Press reported.

Shiite Groups

Shiite groups have clashed in a struggle for supremacy in Basra, the site of Iraq's second-biggest oil refinery.

Al-Sadr said he was seeking a ``political'' solution to end the violence, state television reported today, citing a statement from al-Sadr's office.

The cleric, a popular leader among Iraq's Shiite majority, led two uprisings against coalition forces in 2004. He declared a cease-fire in August after fighting among rival Shiite factions in the holy city of Karbala that killed at least 50 people was largely blamed on his militia.

The U.S. is poised to withdraw about 21,500 soldiers, or five combat brigades, leaving 15 to stay in Iraq. ``There is no change to the current thinking with U.S. strategy in the weeks ahead,'' said Pentagon spokesman Bryan Whitman.

There are 156,000 troops in Iraq today. The second of the five combat brigades to constitute the 2007 surge in U.S. forces in Iraq, the 2nd Brigade of the 82nd Airborne Division, is scheduled to be out of Iraq next week, Whitman said.

Bush will announce his decision on future troop numbers after General David Petraeus, the top U.S. commander in Iraq, and Ambassador Ryan Crocker, testify before Congress on April 8-9.

To contact the reporter on this story: Robin Stringer in London at rstringer@bloomberg.net; Camilla Hall in London at chall24@bloomberg.net.

Last Updated: March 28, 2008 13:06 EDT