The U.S. military says another 3,700 American troops have arrived in the Iraqi capital to support the security crackdown launched in Baghdad in mid-February. 

A statement Wednesday says the new brigade will help Iraqi security forces clear, control and retain key areas of Baghdad in order to reduce violence.

Residents gather around the wreckage of a minibus in Mahmoudiya, about 30 kilometers (20 miles) south of Baghdad, Iraq, Wednesday, 2 May 2007

This is the fourth additional combat unit deployed in Baghdad as part of plans to add some 28,000 troops there.

In violence Wednesday, Iraqi police say 11 people were killed when a bomb exploded inside the bus that was taking them to the town of Hilla, south of Baghdad.

Police say another three people were killed and at least 15 wounded by mortar shells in the town of Mahmudiya, also south of the capital.

Separately, the U.S. military says coalition forces detained 12 terrorist suspects during overnight raids in Baghdad and al-Anbar province.

On Tuesday, U.S. and Iraqi officials said they were trying to confirm reports that al-Qaida in Iraq leader Abu Ayyub al-Masri was killed in a clash among members of his insurgent group.

An Iraqi Interior Ministry spokesman said intelligence reports indicate Masri was killed in fighting north of Baghdad.  But an al-Qaida-linked militant group in Iraq (The Islamic State of Iraq) said Masri has not been killed.

Masri, an Egyptian, assumed the leadership of the terrorist group after Jordanian militant Abu Musab al-Zarqawi was killed in a U.S. airstrike in June 2006.

Some information for this report was provided by AFP and Reuters.