The diplomats were killed after the Taleban stormed the northern Afghan city of Mazar-e-Sharif last month.

Correspondent Rob Watson: Security Council urges maximum restraint on all sides

The Security Council said the murders had seriously increased tension in the region and were a flagant violation of international law.

It demanded the Taleban release those Iranians still being detained in Afghanistan and accept a UN-aided investigation into the killings.

The Security Council also expressed deep concern at what it describes as the escalating military operations in Bamiyan province and reports of mass killings of civilians in northern Afghanistan.

Ali Khamenei: warning

A BBC correspondent, Rob Watson, says the UN's greatest concern is clearly the rising tension between the Taleban authorities and Iran.

Iran has moved thousands of troops to its border with Afghanistan, and Iran's supreme leader, Ayatollah Khamenei, has now ordered them to be on full alert.

Taleban warns Iran

Earlier, Afghanistan's Taleban militia warned it would hit Iranian cities if attacked.

Jim Muir: "Relatives are demanding revenge"

The warning came a few hours after the bodies of seven Iranians killed by the Taleban were returned home.

Senior Iranian government officials have vowed revenge for the killings.

But Taleban spokesman Wakil Ahmed told the Afghan Islamic Press: "Iran must know that if the soil of Afghanistan is attacked, we will target Iranian cities and the entire responsibility will rest with Iranian authorities.

"We do not want a war with Iran, but if Iran attacks we will take all possible necessary measures."

He said the Taleban had reinforced border positions to counter an Iranian military build-up the other side.

Iran has a quarter of a million troops on the Afghan border for military exercises. Commanders have said their forces are prepared to push deep into Afghanistan if ordered.