BRITISH special forces have crossed into Iran several times in recent months as part of a secret border war against the Iranian Revolutionary Guard’s Al-Quds special forces, defence sources have disclosed.

There have been at least half a dozen intense firefights between the SAS and arms smugglers, a mixture of Iranians and Shi’ite militiamen.

The unreported fighting straddles the border between Iran and Iraq and has also involved the Iranian military firing mortars into Iraq. UK commanders are concerned that Iran is using a militia ceasefire to step up arms supplies in preparation for an offensive against their base at Basra airport.

An SAS squadron is carrying out operations along the Iranian border in Maysan and Basra provinces with other special forces, the Australian SAS and American special-operations troops.

They are patrolling the border, ambushing arms smugglers bringing in surface-to-air missiles and components for roadside bombs. “Last month, they were involved in six significant contacts, which killed 17 smugglers and recovered weapons, explosives and missiles,” a source said. It was not clear if any of the dead were Iranian.

Last week, Bob Ainsworth, the armed forces minister, said the Ministry of Defence was unable to say whether British troops had killed or captured any Iranians in Iraq. The ministry declined to comment, but privately officials insisted British troops never carry out hot pursuit across the border.

There have been persistent reports of American special-operations missions inside Iran preparing for a possible attack. But the sources said British troops were solely stopping arms smuggling.

The fighting comes amid an increase in US and British intelligence operations against Iran. Britain’s forces have more than 70 Farsi experts monitoring Iranian communications, and the intelligence is shared with the United States.

Seven American U2 spy planes have passed through RAF Fairford in Gloucestershire this year on their way to Akrotiri in Cyprus or Al-Dhafra in Abu Dhabi, the bases for flights over Iran.

The Al-Quds force has been increasing its arms supplies to both the Shi’ite militias in Iraq and the Taliban in Afghanistan. Officially, Britain has been careful not to blame the Iranian government.

But senior British officials have confirmed to The Sunday Times that it would not happen without the backing of the Iranian leadership.

They pointed out that Gen Qassem Suleimani, the head of the Al-Quds force, has direct access to Ayatollah Khamenei, supreme leader of Iran

Liam Fox, the Conservative defence spokesman, said: “Increasingly Iran poses a direct threat to our armed forces and our wider interests . . . they are playing a very dangerous game.”

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