A bomb hidden inside a softball bat exploded Saturday during a U.S.-Chile game, killing a Canadian and injuring three others, including two American Embassy representatives, officials said.

A man claiming to speak for the Chilean branch of the Palestine Liberation Organization claimed responsibility for the blast in a telephone call to a radio station. The caller warned President Bush not to visit Chile, as he plans to do during a South American tour Dec. 2-8.However, a spokesman for the PLO's office in Santiago denied the group was responsible for the bombing. "We completely, emphatically deny that the PLO acted in the attack," he said, refusing to give his name.

The attack, the second on Americans in Chile in two weeks, occurred during a game at the National Stadium between teams from the U.S. Chamber of Commerce and a Chilean university.

Police said the softball bat was stuffed with nearly a pound of dynamite and exploded in the dugout of the chamber team. The blast killed James Thomas, 36, an executive with a Canadian firm exporting seafood from Chile, they said.

Several terrorist bombings in Chile have targeted buildings belonging to The Church of Jesus Christ of Latter-day Saints.