BAGHDAD, Jan 29: A rocket hit a US embassy compound in Baghdad's fortified Green Zone on Saturday, killing two Americans and wounding four, an embassy spokesman said.

The rocket struck shortly after dark on the eve of Iraq's election, causing an explosion heard across Baghdad. Sirens sounded in the Green Zone shortly after the attack.

"It hit near the embassy building," spokesman Bob Callahan said, referring to Saddam Hussein's sprawling former Republican Palace where most US officials work. "There are two dead and four who are wounded ... all Americans."

US ambassador John Negroponte and other senior staff work in the main embassy in a different part of the Green Zone.

Mr Callahan said he believed the explosion at the embassy annexe was caused by a rocket, not a mortar round, adding that an investigation had been launched.

The US embassy was previously hit by mortar fire in August, when two people were wounded but no one was killed.

Guerillas frequently fire mortars and occasionally rockets into the Green Zone, a vast compound on the west bank of the Tigris River, which is home to the interim government as well as the US and British embassies.

Many embassy staff are housed in prefabricated trailers which are protected by blast walls and sandbags but are open to aerial assault. It was not clear if Saturday's attack hit trailers or just landed near the embassy annexe. -Reuters