Three US soldiers were killed by a roadside bomb west of Baghdad on Thursday and a fourth was killed in a separate attack northwest of the capital, the US military said on Friday.

The three soldiers, from Regimental Combat Team 8, 2nd Marine Division, II Marine Expeditionary Force (Forward), were killed when a roadside bomb struck their patrolling convoy on Thursday near the village of Nasser Wa Salam, some 40 km west of Baghdad, the military said in a statement.

US troops then killed two insurgents and detained four others suspected of involvement in the attack, the statement added.

Another US soldier died of wounds sustained in "an indirect fire attack" in Hit, some 150 km northwest of Baghdad, the statement said.

The names of the killed soldiers were being withheld pending notification of next of kin, the statement added.

The latest deaths brought to 1,992 the number of US soldiers killed in Iraq since the US-led invasion began in March 2003.

Source: Xinhua