The U.S. military says violence in Iraq has killed three American soldiers near the southern port city of Basra.

A statement released Friday says the troops were killed during an attack on a coalition base.

The statement says the troops were killed by "indirect fire" late Thursday.  The U.S. military often refers to mortar and rocket attacks as "indirect fire".

Violence in the region has dropped sharply since coalition and Iraqi forces moved to take control of Basra from Shi'ite militias last year.

On Tuesday, the top U.S. military commander in southern Iraq Colonel Butch Kievenaar warned that some of the Shi'ite fighters who fled to Iran have started to return to the area.

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