By Frances Harrison
BBC News, Tehran
Iran has summoned the Swiss ambassador, who represents US interests in Tehran, to protest against what it calls an American spy network operating in Iran.
Iran's foreign minister has described US policy as "wrong"
The strong protest comes on the eve of talks in Baghdad between the US and Iran over the future security of Iraq.
The US accuses Iran of destabilising Iraq, but now Tehran accuses the US of using Iraqi land to destabilise Iran.
Iran first alleged that the US and its allies in Iraq were running spy networks into Iran on Saturday.
Now it is taking the issue one step further by calling in the Swiss ambassador, who represents US interests in Tehran in the absence of any diplomatic relations.
According to state media the ambassador heard a strong protest against what Iran called "the hostile intervention of the US government".
He was told Tehran had unearthed a number of spy networks aiming to infiltrate Iran and carry out sabotage actions in the west, south-west and centre of the country.
Iran has complained in recent years that a series of bomb blasts in the border province of Khuzestan were carried out by forces backed by the British in southern Iraq.
Now Tehran is pointing the finger of blame squarely at the Americans, on the eve of the first open bilateral talks between the countries for decades.
There are many hardliners who do not want the talks to go ahead, even though their importance is probably more symbolic than anything else.
The Iranian allegations also occur at a time when a number of prominent Iranian-Americans have been arrested on suspicion of espionage and trying to foment a "velvet revolution" in Iran to topple the clerical regime.