While not condemning Israel's attack, the Bush administration is expressing concern over the assassination of a founder of the Palestinian group Hamas.
The White House and the State Department both say they're "deeply troubled" by the incident. State Department spokesman Richard Boucher says the attack increases tensions and will make it harder to pursue peace in the Middle East.
National Security Adviser Condoleezza Rice says the U.S. had no advance warning of the Israeli air strike, and Israel's foreign minister, visiting Washington, agrees that no warning was given.
Ahmed Yassin and two of his bodyguards were killed by a missile attack as they left a mosque. Bush administration officials are urging restraint on both sides, while European nations and the United Nations have flatly condemned Israel.