Hague's telephone conversation with Zarif comes amid reports by a senior US administration official said talks between the United States and Iran about possible cooperation might take place on the sidelines of nuclear talks in Vienna beginning Monday.

The Foreign Office declined to discuss the content of Hague's call. He was due to brief the House of Commons on the situation later Monday.

A spokesman for Prime Minister David Cameron said: "We have contact with the Iranian government and I think one of the things the foreign secretary will say in the house today is that he discussed a number of bilateral issues, including this, with his Iranian counterpart over the weekend."

Earlier, Hague insisted that Britain would not intervene militarily to help Iraq fight the ISIL terrorists, who have overrun swathes of the country in a matter of days.

"We are not planning a military intervention by the UK in this situation," Hague told BBC radio.

Asked whether Britain could participate in air strikes, Hague said he "could not be clearer" that this would not happen.

"The United States is much more likely to have the assets and capabilities for any outside intervention than the United Kingdom," he said.

But first and foremost the onus lay on the Iraqi security forces to stabilize the situation, he said.

NJF/NJF