BAGHDAD, Iraq - Thousands of Shiite Muslims rallied today in the southern city of Basra to show support for Iraq's new constitution and the Shiite-dominated government. The U.S. military said three American soldiers were killed in action in Baghdad and south of the capital.

Also today, five Iraqi soldiers were killed and nine wounded in a bombing targeting their convoy near Beiji, 150 miles north of Baghdad, the Iraqi military said.

The demonstration by at least 5,000 people in Basra, the country's second largest city, was organized by the Supreme Council of Islamic Revolution in Iraq and the Shiite Dawa Party. It was larger than the rallies Sunni Arabs have staged against the constitution in recent weeks.

The two parties are the largest Shiite political groupings in Iraq, and their representatives played a key role in drafting the new charter, the subject of a referendum on Oct. 15.

Demonstrators chanted "Yes to the constitution" and carried banners that said: "The constitution is a guarantee for better future," and "Freedom and justice will be achieved by this constitution."

In Ramadi, a Sunni city west of Baghdad, several hundred people demonstrated against the constitution, chanting "We are brothers, Sunnis and Shiites. We will never sell this country."

In continuing sectarian violence, unidentified gunmen opened fire on Sunni Muslim worshippers at prayers today in two mosques south of Baghdad, killing two people and injuring four, police said.