By Jim Muir BBC Tehran correspondent

Iran's supreme leader, Ayatollah Ali Khamenei, has ruled out negotiations with the United States as a way of resolving current tensions between the two countries.

Rebuff for Senator Biden

The Ayatollah's remarks came five days after the chairman of the US Senate Foreign Relations Committee, Joseph Biden, had offered to open talks with members of the Iranian parliament and intellectuals.

The offer was cautiously welcomed in reformist circles but strongly attacked by hardline conservatives.

In important matters of foreign affairs, the supreme leader's word is final, and this appears to be it as far as taking up Senator Biden's offer is concerned.

Enemy 'aggression'

Ayatollah Khamenei told a gathering of senior officials that negotiations were not the way to a solution and would not settle any problem.

Those whose thoughts turned to negotiations when they were under threat, he said, were betraying their own weakness and incapability.

The only way to confront the American threat, he argued, was to strengthen the system and prepare for a comprehensive defence.

The most important factor encouraging enemy aggression, he added, was the appearance of differences among Iranian officials, whose duty it was to stand firm against the threat.

Dialogue 'ruled out'

Differences had indeed emerged.

The Ayatollah was speaking just a day after the spokesman of President Khatami's reformist government had said there was nothing wrong with taking up Senator Biden's offer of dialogue with fellow parliamentarians, and that it was time to start dismantling the wall of mistrust between the two countries.

Iran's leadership is divided

Now the tone has hardened and dialogue is effectively ruled out.

President Khatami himself, while repeating his commitment to detente, told the same meeting of officials that American politicians should not imagine that they would find anyone in Iran who would raise his hands in surrender from a position of weakness.

And the Iranian Foreign Ministry spokesman said that Senator Biden would be better off addressing his own government's hostile policies towards Iran.

Reformist disappointment

Ayatollah Khamenei's unambiguous declaration will come as a big disappointment to the reformists; they had been hoping to persuade him to support an opening to Washington in the hope of defusing US hostility.

Some are convinced that the Americans do intend to bring about a change of regime in Baghdad and then to turn their sights on Tehran.

They argue that the sooner a dialogue is opened, the better, because if it is left until later, Iran will be in a much weaker position.

But their conservative and hardline opponents have insisted that unity and resolve would see off the American threat.

The supreme leader has come down clearly on their side of the argument.

Without his support, it is clear that no significant dialogue can take place.