Demonstrators carry banners during an anti-war protest in downtown Sana'a on Saturday

SANAA, March 18 (IslamOnline.net & News Agencies) - An American, a Canadian and a Yemeni were shot dead Tuesday, March 18, in an attack by a Yemeni gunman who then killed himself at an oilfield east of Sanaa, local authorities said.

The assailant turned the gun on himself after having killed his three victims in the Safer oil region, some 300 kilometers (190 miles) east of Sanaa, a local official told Agence France-Presse (AFP).

An investigation has been launched on the circumstances of the attack and the motives of the assailant, he added.

The official said the American and the Canadian worked for a Western oil company operating in Safer, situated in Marib province, where Yemeni and U.S. forces have been hunting down suspects in the bombing of the USS Cole warship in October 2000 that left 17 sailors dead.

The shooting came as the United States and Britain step up preparations to invade Iraq to overthrow President Saddam Hussein, whom they accuse of possessing and developing weapons of mass destruction.

Hundreds of thousands of Yemenis have taken to the streets of Sanaa and provincial cities over recent weeks to demonstrate against a U.S.-led war on Iraq .

Three American missionary doctors, of the U.S. Southern Baptist Convention's International Mission Board, were shot dead and a fourth was wounded in the southern Yemeni town of Jibla last December.

Wielding a Kalashnikov assault rifle, a gunman opened fire in the Jibla Baptist hospital in the province of Ibb , 170 kilometers (105 miles) south of the capital Sanaa, the officials said.

The killer, who was arrested, entered the building saying he was visiting a sick relative. But he gunned down the doctors as they held a routine morning meeting, the officials added.

In November, a Yemeni gunman opened fired at a helicopter belonging to U.S. oil independent Hunt Oil Company, shortly after its takeoff from Sanaa airport, injuring one American.

In October, 2002, a small boat packed with explosives rammed and badly holed a French supertanker off Yemen, in what appeared to be a re-run of the attack on the USS Cole destroyer.