US officials are expected to call on Iran to stop arming and funding Shi'ite militias when Iranian and American diplomats hold rare talks in Baghdad on Monday to discuss how to curb sectarian violence in Iraq.
Iran denies the charge, despite the US military putting on display what it says are Iranian-made rockets, mortars and sophisticated roadside bombs seized in Iraq.
US officials do not expect any great breakthrough from the talks, which come as US warships hold war games in the Gulf and Tehran said it had uncovered spy networks on its territory run by the United States and its allies.
The Iranian Foreign Ministry on Sunday summoned the Swiss ambassador to Tehran, who represents US interests in Tehran, to voice its displeasure at the spy networks.
US President George W Bush called last week for stronger sanctions against Iran over its nuclear program, which Washington says is being used to develop a nuclear bomb.
But Iran's atom program will not be up for discussion on Monday. Only one item will be on the agenda -- Iraq, where sectarian violence between minority Sunnis and majority Shi'ites threatens all-out civil war that could spill into the region.
The talks between US ambassador Ryan Crocker and his Iranian counterpart Hassan Kazemi-Qomi mark a reversal by Washington, which broke ties with Tehran in 1980 and has largely sought to isolate the Islamic Republic in recent years.
Crocker has said he does not expect "any stunning, startling breakthroughs" from the meeting. US officials say he will press Iran to take steps to reduce violence in Iraq.