KABUL, Afghanistan -- Atomic experts came to Afghanistan this week after radioactive cobalt-60 was found in the abandoned wing of a hospital -- a discovery that raised fears other dangerous materials might lie forgotten in the country's rubble.

Though radioactive materials can be used to make "dirty bombs," there was no evidence the cobalt-60 was intended for anything but medical treatment or that it had been tampered with by al-Qaida or the Taliban, said Capt. James Cameron, head of the peacekeepers' nuclear, biological and chemical monitoring group.

The team, acting on information from Afghan authorities, discovered the cobalt-60 at the hospital in the western part of Kabul, Cameron said. It was housed in a machine for treating cancer and was located in an abandoned wing of a hospital -- surrounded by 10-foot-thick, lead-lined walls.

The doors of the room were open, and the machine where the cobalt-60 was stored had been pried open. Cameron said the tampering had probably been done a decade ago during factional fighting that destroyed large parts of the hospital.

International peacekeepers closed up the machine and sealed the room.

Finds of such dangerous materials are cause for concern, experts said.

"These sources are very worrying, and particularly in Afghanistan," said Tom Clements, executive director of the Nuclear Control Institute in Washington.

U.S. officials have sounded the alarm about the threat posed by so-called dirty bombs since Sept. 11, and regulatory authorities have called for greater monitoring of radioactive materials that could be used to make them.

The devices use explosives to scatter radioactive material. They are not nuclear bombs, but could contaminate populated areas and cause disease and panic, experts say.

Investigators believe the medical equipment was brought to Afghanistan by the Soviets in 1978. The material inside measured a still-potent radiation reading of more than 300 curies last week, Cameron said.

A three-member team from the Vienna-based International Atomic Energy Agency arrived on Monday to investigate after the peacekeepers determined they couldn't handle such the radioactive materials on their own.

The agency team also toured an out-of-use physics laboratory at Kabul University that contained several radioactive isotopes that could be dangerous in the wrong hands, Cameron said.

The energy agency team determined that no hazardous radiation had contaminated the laboratory or the hospital, but nevertheless recommended both be secured, a U.N. official said, speaking on condition of anonymity.

On Monday, crews were to begin transporting the materials from the physics lab to the hospital wing so they could be safely stored in the lead-lined room, Cameron said.

The materials eventually will have to be removed to ensure they don't leak or fall into the wrong hands, but it will be a multimillion-dollar operation, Cameron said.