The United States denied Monday it had given the green light to Israel to kill Hamas leader Sheikh Ahmed Yassin and appealed for calm in the region following the assassination.
White House national security advisor Condoleezza Rice also said in morning television shows the United States did not have advance warning of the assassination from Israeli Prime Minister Ariel Sharon.
"It is very important that everyone step back now and try now to be calm in the region. There is always a possibility of a better day in the Middle East and some of the things being talked about by the Israelis - about disengagement from areas - might provide new opportunities," Rice told NBC's "Today" show.
"I would hope that nothing will be done to preclude those new opportunities from emerging," she added.