Secretary-General Kofi Annan condemned on Friday the murders of nine Iranian diplomats in Afghanistan, called for an urgent investigation and said the country's Taliban rulers had asked him to mediate in their conflict with Tehran.

Annan also appealed to the Taliban to ensure the safe return of two other Iranian diplomats and a journalist who are still missing, saying he would cooperate in that venture.After denying knowledge of the diplomats for weeks, the Taliban's spiritual leader, Mohammad Omar Mujahid, told Annan the Iranians were killed after Taliban militia seized the northern city of Mazar-i-Sharif on Aug. 8 "by unidentified soldiers who acted on their own."

Since the diplomats disappeared, Iran has built up its forces on its border with Afghanistan.

"We ask the United Nations to resolve the issue according to the international rules and laws," the Taliban letter said. "If the issue is not resolved through the mediation of the United Nations, the Islamic Emirate of Afghanistan will not bear the responsibility of the consequences that may follow."

"The secretary-general strongly condemns these cruel murders and violations of international law," a U.N. statement said. "He calls for an urgent investigation so that the perpetrators can be brought to justice.

The United Nations is attempting to organize a fact-finding mission in conjunction with Iran and Pakistan on the killings. Iran requested the probe, and Pakistan, an ally of the Taliban, agreed. U.N. officials are determining whether security can be guaranteed.

Annan did not say what other kind of mediation the United Nations might undertake in response to the request by the Taliban, which controls most of Afghanistan.

"While the United Nations is ready to do anything at its disposal to defuse the increasing tension, the secretary-general calls on the Taliban to cease all military activities in Afghanistan immediately and without any pre-condition," he said.

On Thursday, Security Council members condemned the killings and also asked for an "urgent investigation into these crimes" in order to bring the perpetrators to justice.