We are making our utmost effort, but the reality is that it is not possible to control this long border completely

Iran's foreign minister

But he acknowledged that the long, remote and largely mountainous border was impossible to seal and said Washington should provide Iran with any information it had - instead of launching propaganda attacks on Iran.

Mr Kharrazi admitted that narcotics smugglers and migrants had continued to enter Iran from Afghanistan despite strenuous Iranian efforts over many years to stop them.

Letter to Annan

He urged the United States to share any information they had so that Iran could take action.

Any al-Qaeda or Taleban members caught in Iran, he said, would be handed back to the authorities of their own countries.

Kharrazi said US should help Iran catch al-Qaeda members

As the war of words intensifies between Washington and Tehran, Mr Kharrazi has also sent a long letter to the United Nations Secretary General, Kofi Annan, denouncing what he called unfounded allegations and threats of force against Iran by the Americans.

He said Israel had succeeded in hijacking the American war against terrorism and turning it into unconditional US support for its own occupation and brutal suppression of the Palestinians.