Foreign Ministry spokesman Hamid Reza Asefi also denied suggestions made by some US officials in recent days that Iraqi Governing Council member Ahmad Chalabi had passed sensitive US intelligence about Iraq to Iran.

"We have warned the Americans about Iraq," Asefi told a weekly news conference. "It is natural for two countries which do not have diplomatic relations to exchange messages."

Asefi did not comment on the contents of the warning, but officials and religious leaders in Shia Muslim Iran have expressed outrage in recent weeks about the presence of US-led forces in the holy Shia Iraqi cities of Najaf and Kerbala.

Asefi said the diplomatic message was sent via the Swiss Embassy in Tehran, which represents US interests in Iran. Washington broke ties with Iran in 1980.

Asefi described as "baseless" accusations made by unnamed US officials in some US media that Chalabi -- whose Baghdad headquarters were raided by US troops and Iraqi police last week -- had leaked information to Iran that the officials said could "get Americans killed."

"We have not received any classified information, neither from Chalabi nor any member of the Iraqi Governing Council," he said.

"What is going on between us and members of the Iraqi Governing Council and all groups in Iraq is negotiation, the exchange of views and clear and transparent cooperation."

Asefi said the accusations against Chalabi, a former favorite of the Pentagon, were part of an effort to deflect attention away from Washington's problems in Iraq.

AFP adds: Demonstrators attempting to storm the British embassy in Tehran yesterday clashed with riot police guarding the building in the fourth such incident in a week, an AFP journalist witnessed.

Some 400 Islamic students pelted stones at the embassy, demanding the withdrawal of British forces from Iraq and the expulsion of the British ambassador.

Hundreds of police formed a cordon around the embassy to stop the demonstrators approaching.

The protestors who gathered after a call by Islamic militias at universities tried to force their way past the cordon around the embassy in the centre of the capital.

They called for the embassy to be closed and British Ambassador Richard Dalton to be expelled. "Go home," they chanted.