Three U.S. soldiers were killed in two separate incidents in northern Iraq, the U.S. military said on Wednesday, the latest casualties in what has been the deadliest year of the war for U.S. forces.

In central Baghdad, a roadside bomb killed two civilians and wounded three just outside the heavily fortified Green Zone that houses the U.S. embassy and government ministries, police said.

The explosion, which shook buildings in the Green Zone, was close to a heavily guarded checkpoint where hundreds of Iraqis who work inside the sprawling complex queue every morning.

It was one of the loudest blasts heard in the capital in weeks after a lull in attacks that had become almost a daily occurrence earlier this year, witnesses said.

The U.S. military said one of its convoys had been the target of the bomb but gave no information about possible casualties. Police said at least one vehicle had been hit.

Two U.S. soldiers died and four were wounded when they were hit by a roadside bomb in restive Diyala province northeast of Baghdad on Tuesday, the military said in a statement. Roadside bombs are by far the biggest killers of U.S. troops in Iraq.

Another U.S. soldier was shot and killed near the volatile city of Mosul, 390 km (240 miles) north of Baghdad.

Their deaths took the total of U.S. soldiers killed in Iraq to 3,863, according to the independent Web site icasualties.org, which tracks military and civilian casualties in Iraq.

Sharp drop

U.S. military and Iraqi civilian casualties dropped sharply in the previous two months, with a boost of 30,000 extra troops, improving Iraqi security forces and the growing use of neighborhood police units being credited for the declines.

However, 860 U.S. troops have been killed so far this year, the worst annual total since the U.S.-led invasion to topple Saddam Hussein in 2003. The previous worst yearly total was in 2004, when 849 U.S. soldiers were killed.

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