Iran is trying to derail an agreement that would allow US and British troops to stay in Iraq after their mandate expires at the end of this year.

In a move that has raised concern among senior Iraqi and US officials, Tehran is using its influence over its smaller neighbour to scupper a Status of Forces Agreement, which must be reached by January 1.

After the deadline US and British troops would have no legal basis to remain and, in theory, would have to leave.

This week President Ahmadinejad told a senior official from Baghdad that Iraq had a duty to rid itself of US forces. Ali Larijani, the Speaker of the Majlis (parliament) gave warning of “unpleasant impacts” if Iraq went ahead with the deal.

Hassan Kazemi-Qomi, the Iranian Ambassador to Baghdad, accused the US of trying to impose the agreement on Iraq and said that Washington was treating the country like a football.

Hoshyar Zebari, the Iraqi Foreign Minister, assured the Iranian Ambassador that the draft agreement included a clause that prevented foreign forces from using Iraq as a springboard for attacks against its neighbours.

He also reminded Iran that the decision was one for Iraq, its parliament and its people. “We expect that our decisions will be respected by all our neighbours,” Mr Zebari said.

Iran has been accused of arming, training and funding militant Shia Muslim groups in Iraq that were responsible for attacks on US and British forces.

Under the current United Nations Security Council resolution the 150,000 US and 4,000 British troops in Iraq have a mandate to remain until December 31.

After that a bilateral agreement must be in place. A draft document has been drawn up but there is still controversy over the wording about immunity for foreign troops serving in Iraq. The document also sets out a timeline in which all US forces could be removed by 2011.

Iraqi leaders are expected to meet next week to decide whether to push through the agreement, which must be ratified by the 275-member Iraqi parliament.

An agreement seemed likely earlier this year but Iraqi and US officials have now given warning that it is complicated by the Iraqi elections in January. While most Iraqi politicians privately accept the need for the Americans to remain, few are prepared to say so publicly, particularly before an election.

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