Tensions between Iran and the Taliban religious army, which controls most of Afghanistan, have been high since the militia admitted that its forces killed eight Iranian diplomats and a journalist after taking over the northern Afghan town of Mazar-e-Sharif in August.

Iran has deployed more than 200,000 troops on its border with Afghanistan, and Taliban leaders say they have moved 20,000 troops to the frontier.

``Our patience is limited and we hope that we will not be compelled to resort to other means,'' the television quoted Foreign Minister Kamal Kharrazi as saying.

The Taliban still holds some 50 Iranians.

Kharrazi said the Taliban must release the detained Iranians and return the bodies of those who have been killed.

He spoke at a meeting with visiting UNenvoy Lakhdar Brahimi.

The Taliban has said that renegade fighters killed the Iranians but has refused to hand the killers over to Iran. The militia controls some 90 per cent of Afghanistan.

Iran is believed to be arming and financing the Taliban's northern-based opposition, which includes the country's minority Shiite Muslims. Most Iranians also are Shiite Muslims.

The Taliban is made up largely of ethnic Pashtuns, who are mostly Sunni Muslims.

The UN envoy had met senior United Arab Emirates (UAE) leaders in Abu Dhabi last week and is due to reach Islamabad on Thursday for talks with Pakistani officials as well as Taliban representatives.

Reports from Tehran said Brahimi was expected to meet Iranian president Mohammed Khatami today.

The mission is a joint effort by the UN and the Organisation of the Islamic Conference (OIC) amid increasing international concern over the situation on the Iran-Afghanistan border.

The decision to send the mission was taken after a meeting between UN SecretaryGeneral Kofi Annan and OIC Secretary General Ezzeddine Laraki in New York last week.

Tension has been growing between Iran and the Taliban since the nine Iranians were killed after the Taliban captured the northern Afghan city of Mazar-e-Sharif on August 8.

The militia said the diplomats and the journalist were killed by some of its fighters acting without orders.

Last month, some 70,000 Iranian troops conducted major military exercises near the country's border with Afghanistan.

Iran is now planning its largest ever military exercises in the area later this month and has amassed about 200,000 troops near the border, causing serious concern in the region and elsewhere. The Taliban, on its part, has warned Tehran of ``serious steps'' if it interfered in Afghanistan's affairs.

``If this interference continues, then our people would take serious steps,'' media reports quoted Taliban leader Mohammed Omar as saying.