The White House says it had no advance knowledge of plans by Israel to kill Hamas leader Sheikh Ahmed Yassin. U.S. officials called on all sides in the region to exercise restraint.

White House National Security Advisor Condoleezza Rice says the United States had no advance warning of the assassination.

During an appearance on NBC television's Today show, she denied President Bush was informed by Israeli leaders that an attack was imminent.

"Let's remember that Hamas is a terrorist organization and the Sheikh Yassin has himself, personally, we believe, been involved in terrorist planning. But of course, the United States did not have advance warning," she said.

Ms. Rice did not specifically condemn the attack on the Hamas leader, who was killed along with seven other people as he left a mosque early Monday in the Gaza Strip. However, she did call on Israelis and Palestinians to remain calm and focus on the need to move the peace process forward.

"There is always a possibility of a better day in the Middle East and some of the things that are being talked about by the Israelis about disengagement from areas might provide new opportunities. So I would hope that nothing would be done that would preclude those new opportunities from emerging," she said.

White House spokesman Scott McClellan carried on that theme a short time later at a briefing for reporters. He said the Bush administration is concentrating on getting the Israelis and Palestinians to keep moving toward the vision of a two-state solution.

Mr. McClellan said the administration is in constant contact with all parties in the region, but he too rejected the notion that somehow the United States had given Israel the go-ahead to kill the Hamas leader. As he put it: "we are not a traffic cop. . . we do not give a green light."