ISLAMABAD, Pakistan (AP) _ The United Nations made an exception to its ban on travel to Afghanistan to allow an envoy to meet the Taliban's reclusive leader and try to defuse a border standoff with Iran, a senior official said Tuesday.

Lakhdar Brahimi will travel to the Taliban heartland in southern Kandahar on Wednesday and meet with Taliban chief Mullah Mohammed Omar.

Despite the ban, he got permission from U.N. Secretary-General Kofi Annan because ``the stakes are much too high'' in the troubled region, said James Ngobi, acting head of the U.N. special mission headquarters in Pakistan.

Brahimi, a former Algerian foreign minister, will be the first special envoy sent by the secretary-general to meet Omar.

Before Brahimi agreed to go to Kandahar, the Taliban promised him a ``full explanation'' for attacks on U.N. workers, including the killing of an Italian official in August, said Ngobi.

The Taliban leader rejected several attempts by Brahimi's predecessors for a face-to-face meeting. Omar's control over the hard-line Taliban militia that rules 90 percent of Afghanistan is undisputed.

Brahimi is in the region to find a peaceful end to the standoff between the Taliban religious army and neighboring Iran, which deployed 200,000 soldiers to its border with Afghanistan after several of its diplomats were killed by renegade Taliban soldiers in August.

The Taliban leader has rejected several attempts by Brahimi's predecessors for a face-to-face meeting. Omar's control over the hard-line Taliban militia that rules 90 percent of Afghanistan is unchallenged.

Meanwhile in Tehran, an Iranian official said Tuesday that his government has detected a change in the Taliban's attitude and would not oppose a visit to Iran by a militia representative, state-run Iranian radio reported.

The report quoted Deputy Foreign Minister Mohsen Aminzadeh as attributing the change to pressure from the United Nations, the international community and Iran's decision to mass troops at the border.

The United Nations pulled its international staff out of Afghanistan after the Italian was shot and killed, apparently in retaliation for the U.S. missile attack on suspected terrorist camps in eastern Afghanistan.

``The Taliban until now have not been able to explain the circumstances of the U.N. workers who have been murdered, shot at and harassed. . . we said we do not go back until these things are addressed,'' Ngobi told The Associated Press in an interview.

Tehran is demanding an apology from the Taliban, whose forces killed the diplomats, and the return of an estimated 50 Iranians being held in Kandahar by the Taliban.