WASHINGTON, May 19: The United States is "very concerned" about the number of Palestinians killed in Israel's major military raid in the Gaza Strip and has sought answers from Israel, the White House said on Wednesday.

"We are very concerned about the reports from Gaza and the number of Palestinians who are said to have been injured and killed," spokesman Scott McClellan told reporters in a sharp escalation of US rhetoric.

"We have asked the government of Israel for the facts about what happened today. We will continue to follow this closely and we urge all parties to exercise maximum restraint," he said. "We want to know the facts."

At least 34 Palestinians have been killed since Israel launched its massive "Operation Rainbow" in the Palestinian refugee camp of Rafah, saying it means to smash tunnels used to smuggle weapons under the border with Egypt.

Amid reports that Israel intended to bulldoze hundreds of homes to widen a buffer zone on the border with Egypt, McClellan said Israel knew "very well" that Washington opposes "the destruction of homes of innocent Palestinians."

The sterner rhetoric towards Israel came a day after US President George W. Bush had said the operation was "troubling" but reaffirmed his belief that Israel had a right to target extremists.

Mr Bush told a powerful pro-Israel group, the American Israel Public Affairs Committee (AIPAC), that "The unfolding violence in the Gaza Strip is troubling and underscores the need for all parties to seize every opportunity for peace."

"The United States is strongly committed, and I am strongly committed, to the security of Israel as a vibrant Jewish state. Israel is a democracy and a friend, and has every right to defend itself from terror," he said in a speech.

And Mr McClellan had said later that the United States understood Israel's reasons for the raid in the Palestinian refugee camp of Rafah, which it said was to smash tunnels used to smuggle weapons under the border with Egypt. -AFP