The United Nations has launched an investigation into Israeli charges that Palestinian militants have used U.N. ambulances to transport weapons. The issue is turning into a brewing feud between Israeli officials and U.N. aid workers in the Gaza Strip.

Secretary General Kofi Annan has ordered an immediate probe into allegations made by Israeli officials that a U.N. van was used to transport rockets for use against Israel.

Mr. Annan's action followed the release of a video taken by an unmanned Israeli aircraft flying over the Jebaliya refugee camp in Gaza that shows an object being loaded into a U.N. ambulance. Israel says a study of the video indicates the object was a homemade Kassam rocket like those used by Palestinian militants.

The head of UNRWA, the U.N. Relief and Works Agency for Palestine, immediately rejected the charges. In a statement, UNRWA chief Peter Hansen called the Israeli allegations "deliberately inciteful, false and malicious propaganda."

U.N. Spokesman Fred Eckhard told reporters a preliminary UNRWA investigation had concluded the object loaded into the van was not a rocket. "After reviewing the videotape and interviewing the ambulance driver, UNRWA concluded that the object visible on the tape is a folded stretcher," he said. "It appeared to be the wrong length and much too light in weight to be a missile."

Secretary-General Annan called in Israeli Ambassador Dan Gillerman Monday to ask for evidence to back up Israel's claim that the object was a rocket. Afterward, Ambassador Gillerman told reporters Israeli intelligence had used sophisticated means to analyze the tape.

"I can tell you that the Israeli army is convinced that the object put into that U.N. vehicle was indeed a weapon and not a stretcher," he said.

Ambassador Gillerman also criticized UNRWA chief Hansen, accusing him of allowing the U.N. agency to be used by the Palestinian terrorist group Hamas. In an earlier interview with Canadian television, Mr. Hansen had said he was sure there are Hamas members on the UNRWA payroll, but noted a distinction between the group's political and military wings.

The Israeli ambassador called the distinction unacceptable, and suggested the world body is taking sides in the Israeli-Palestinian conflict. "What we see here is a very worrying pattern of U.N. involvement in terrorist activities," he said. "Too many times has the U.N. found its staff, personnel, vehicles or its logistics too near to terrorist activity, or being used or maybe even cynically manipulated by terrorists, and the mere fact that this is happening time after time is something the U.N. should be very worried about."

In reply to a question about Mr. Hansen's comments about Hamas Monday, U.N. spokesman Eckhard replied "We don't hire terrorists." He said if any U.N. staff members were involved in any illegal action, the world body would take disciplinary and legal action.