Baghdad, Iraq ? A suicide driver set off a truck bomb at the gates of the U.S.-led coalition headquarters Sunday, killing about 20 people and wounding 63 in the deadliest attack here since Saddam Hussein’s capture last month.

The bombing came on the eve of a meeting between U.S. administrator L. Paul Bremer and U.N. Secretary-General Kofi Annan to discuss Iraq’s future, including whether Iraq is safe enough for the world body to return.

Witnesses said that at about 8 a.m., the driver of what the U.S. military described as a white Toyota pickup truck tried to bypass a line of Iraqi workers and a crowd of U.S. military vehicles, coming as close as possible to the entrance American troops call “Assassins’ Gate.”

The attack was the first vehicle bombing inside the U.S.-controlled “Green Zone” along the west bank of the Tigris River, which insurgents have targeted in the past with mortar and rocket fire.

Most victims were Iraqis, waiting in cars or lined up for stringent security checks before going to work or attending other business inside the high-walled coalition compound.

The U.S. military command said about 20 people were killed and more than 60 wounded, including three U.S. civilians and three American soldiers. The military initially reported two of the dead were Americans working for the Pentagon but later said their nationalities were unknown and they were not Defense Department employees.

The attack occurred one day before Bremer, Annan and U.S.-appointed Iraqi officials are to meet at the United Nations in New York to discuss possible solutions to a political deadlock over a U.S. plan to hand over power to a provisional Iraqi government by June 30.

The Bush administration, which had shunned U.N. involvement in Iraq, has signaled it is now anxious for the world body to play a role as Washington prepares to hand over sovereignty to a new Iraqi leadership by June 30.

Annan withdrew all international U.N. staff from Iraq after two bombings at U.N. headquarters and a spate of attacks on humanitarian targets. Annan’s concern has been whether the situation was secure enough.

U.S. soldiers help a crying Iraqi man away from the scene of a car bomb that exploded outside the main gate to the headquarters of the U.S.-led coalition. Sunday's attack killed about 20 people, U.S. military leaders said.