"I just think what we are seeing here is a terrible human tragedy," William Burns, assistant secretary of state for the Near East, told Reuters in the camp's flattened center.

As relief agency officials and human rights activists swarmed around the camp, an Israeli Arab doctor stepped on something that exploded, blowing him off his feet.

Writhing in agony and bleeding from the leg, Wael Omari, part of a delegation of physicians, was stretchered away to an ambulance by shocked colleagues. The blast was a sharp reminder of the dangers posed by unexploded ordnance and booby-traps.

"It's obvious that what happened here in the Jenin camp has caused enormous human suffering for thousands of Palestinian civilians," said Burns, the most senior U.S. official to visit the camp since Israeli forces pulled out on Friday.

Burns, who was accompanied by United Nations officials and armed bodyguards, stopped occasionally to gaze at refugees digging furiously at the wreckage of their homes in search of missing loved ones and cherished possessions.

Heavy rain had churned the camp's dirt roads to mud, but failed to drown the smell of rotting corpses that still lie beneath the mounds of pulverized masonry.

CALL FOR ACCESS

Burns called for aid agencies to be granted free access to the camp. He would not comment on Palestinian accusations that troops committed a massacre in what Israel has called a "nest of terror" and the launch-pad for 23 suicide attacks.

"I think it's vitally important, obvious to anyone who can see, to provide full and complete access to relief agencies so that they can do their work, so that they can get equipment and supplies here," Burns declared.

"It's important that the United Nations is going to launch a fact-finding mission to try to find exactly what happened here with the cooperation of Palestinians and Israelis both."

Burns was speaking hours after the U.N. Security Council voted unanimously to send a fact-finding team to the camp.

Israel says its hands are clean and has pledged to cooperate fully with the U.N. mission.

"The United States is going to do everything it can to help both in terms of relief supplies and equipment," Burns promised.

An Israeli army spokesman said all forces had withdrawn from the camp apart from some soldiers engaged in humanitarian efforts. A spokeswoman for the International Committee of the Red Cross said ICRC staff were observing their activities.

"The Red Cross is functioning as an observer in the Jenin refugee camp, ensuring that the Israeli forces are extracting bodies and delivering them to their families for proper burial, with respect for religious practice," Jessica Barry said.

"It took six days for the Israeli army to let us into the camp, but now we have fairly free access on a daily basis."

Barry said the ICRC knew of several explosions caused by people disturbing objects lying in the debris of the camp.

Two boys aged 13 and 16 were wounded in one such incident on Thursday. One was hurt in the eye and the other in the hand.

On Friday, a woman who was sweeping her floor picked up something which exploded, wounding her.