The attack showed Iraq’s still precarious security situation despite a fall in violence from past levels as US troops prepare to withdraw from the country, more than eight years after the invasion that toppled former dictator Saddam Hussein.

A US statement gave no details of how the US personnel were killed in central Iraq. But a senior Iraqi security official said the Americans were killed when militants fired rockets into a joint base in Baghdad’s Baladiyat district.

“This morning, the American base at Loyalty Camp came under rocket attack. There was a lot of smoke inside and the Americans died in that attack in the Baladiyat area,” the security official, who asked not to be named, told Reuters.

Loyalty Forward Operating Base, on the former site of Saddam’s internal security directorate, is next to Sadr City, the stronghold of Muqtada Sadr.

Two suspected militants involved in the attack were killed when a rocket exploded prematurely on the truck they were using as a launch platform, an Interior Ministry source said.

US forces officially ended combat operations in Iraq last August ahead of a scheduled US troop withdrawal at the end of this year. American troops are now mainly involved in a support and training role, and helping Iraqi security forces in counter-terrorism operations.

US fatalities in Iraq since last year have become more sporadic. Two US soldiers were killed in May.

Violence in Iraq has generally dropped since the height of sectarian conflict in 2006-2007, but gun and bomb attacks still occur daily, often targeting local Iraqi security forces.

At least 13 people were killed on Monday when a suicide bomber detonated a car targeting Iraqi security forces in the central city of Tikrit.

Around 47,000 US troops still in Iraq are due to leave by the end of 2011 under a security pact, and Iraqi Prime Minister Nuri Al-Maliki’s coalition government is debating the sensitive question of whether to ask Washington to keep some of them in place.

US officials and senior Iraqi military commanders have said they believe some kind of continuing US military presence is necessary to ensure Iraq’s security and defense needs, especially in an advisory and training role.