Ayatollah Khamenei and his clique of clerics dominate Iran
Resuming ties with the United States would be tantamount to surrender, Iran's supreme leader has said.
Ayatollah Ali Khamenei also accused the Americans of preparing the ground for an invasion of the hardline Islamic state.
His uncompromising comments came after it emerged that American and Iranian officials have been holding talks in an attempt to reduce tensions between the two nations.
The US broke off diplomatic relations following Iran's Islamic revolution in 1979, and President George W Bush has described the country as part of an "axis of evil" because of its nuclear ambitions and support for militant groups in the region.
The Americans know very well that any adventures in
Iran will fail
Iran is now bordered by two countries whose anti-US governments have been toppled by American military intervention - Iraq and Afghanistan.
Ayatollah Khamenei heads a grouping of conservative clerics who dominate Iran, despite the existence of an elected president and parliament dominated by reformists.
A majority of the members of the 290-seat Iranian parliament recently signed an open letter calling for normal relations between Iran and the outside world, including the US.
But in a speech to thousands of students in the capital Tehran, the ayatollah issued what appeared to be a warning to reformist elements within the country.
"Some are prescribing surrender to the US adventurers, but
surrender to the enemy is no remedy," the state news agency IRNA quoted him as saying.
"To go to the enemy is not the solution, since that would do
nothing but to reinforce his morale, and make him more and more
"To question the effectiveness of Iran's system, as well as our
values and revolutionary beliefs, serves the American interests.
"Unfortunately certain elements, consciously and unconsciously,
are helping the enemy to create the conditions for a (US) military
or partial military action."
According to American diplomats, the meetings in Geneva have focused on a wide range of issues including the future of Afghanistan and the setting up of a government for post-war Iraq.
Iran's support for militant Islamic groups in the Middle East and its alleged nuclear weapons programme may also have been included on the agenda.
Iran's leaders deny any links to al-Qaeda
The US military's decision at the weekend to disarm a heavily armed Iraq-based Iranian opposition group, the People's Mujahedeen, is seen as a gesture towards Tehran.
The Americans, in turn, have reportedly asked the Iranians to hand over suspected members of al-Qaeda who might have fled to Iran from northern Iraq during the war in Iraq.
President Bush's special envoy to Iraq and Afghanistan, Zalmay Khalilzad, has apparently represented the US in the continuing meetings.
But the president's National Security Adviser, Condoleezza Rice, insists that they are not a step towards restoring diplomatic relations.
In an interview with the Reuters news agency, she said there were many barriers to broad diplomatic ties, including what she described as Iran's support for terrorism.
She also reiterated the view of the Bush administration that Iran was failing to comply with a nuclear non-proliferation treaty, and should be cited for non-compliance by the International Atomic Energy Agency.
Iran says its nuclear programme exists for the production of nuclear energy alone.
The US broke off relations with Iran in 1980 after radical students seized its embassy in Tehran following the Iranian revolution.
More than 50 Americans were held hostage in Tehran for