A Yemeni gunman fatally shot three oil workers in Yemen today, including an American, and wounded a fourth before killing himself, according to oil company officials and a U.S. diplomat.

Jim Oberwetter, a spokesman at Hunt Oil Co.'s headquarters in Dallas, said the assailant first killed a Hunt worker, an American supervising drilling operations. The gunman then shot two Canadians, one of whom survived, and a Yemen citizen working for the drilling company before killing himself.

"Hunt has suspended our drilling operations in Yemen for the foreseeable future," he said, adding that the company did not know the killer's motive.

The attack took place in the oil-rich northern province of Marib, about 100 miles northeast of Sanaa, the capital. Both Westerners worked at a Hunt Oil Co. rig and were shot while working in the field, tribesmen and oil workers said.

The motive for the attack was unclear. Violence is not unusual in the largely lawless tribal areas of Yemen, but the country also has been the scene of several Islamic militant terror attacks on Western targets in recent years.

A diplomat at the U.S. Embassy confirmed the shooting and said U.S. security personnel were in contact with the Interior Ministry to obtain more details. "We have reliable information confirming the attack. We know that an American and a Canadian were killed and another Canadian was wounded," he said.

Canadian Foreign Affairs spokesman Reynald Doiron said "preliminary indications do seem to exclude the terrorism angle," but he would not elaborate.

Yemen, long a haven for terrorists, is the ancestral homeland of al Qaeda leader Osama bin Laden.