Mehdi Army fighters attacked police patrols in southern Baghdad, police said, further fraying a seven-month-old cease-fire called by Shiite cleric Moqtada al Sadr to rein in his militia.

The clashes in Baghdad's Shurta district, which started late on Thursday and continued into Friday morning, follow outbreaks of violence in the southern Iraqi city of Kut in which Mehdi Army fighters battled US and Iraqi security forces.

The fighting took place on the same day that Iraq marked five years since the US-led invasion.

A US soldier died from wounds sustained on Friday from "indirect fire", a term usually used to describe rocket or mortar fire, south of Baghdad the US military said. Four other soldiers were also wounded.

Separately, a US soldier died earlier this week when his vehicle overturned in Mandali, a town about 100 kilometres north-east of Baghdad, the US military said.

The deaths bring the number of US soldiers killed in Iraq since the invasion to at least 3,993 according to website www.icasualties.org. War critics are likely to seize on the grim milestone of 4,000 to renew calls for a U.S. troop withdrawal.

- Reuters