Iran has summoned the Swiss ambassador to Tehran, who looks after US interests, over comments by Secretary of State Rex Tillerson backing "peaceful transition" in the Islamic republic.

Bahram Ghassemi, the ministry spokesman, informed Iranian media on Tuesday about the diplomatic protest and said Tillerson's comments were "contrary to international law and the UN charter".

Iran also sent a protest letter to UN Secretary General Antonio Guterres, according to the ISNA news agency.

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Tillerson accused Iran of seeking "hegemony" in the Middle East at the expense of US allies such as Saudi Arabia in last Wednesday's testimony to the House Foreign Affairs Committee.

"Our policy towards Iran is to push back on this hegemony ... and to work toward support of those elements inside of Iran that would lead to a peaceful transition of that government," Tillerson said.

"Those elements are there certainly, as we know," he said, without elaborating on the groups he was referring to.

Revolutionary Guards

In his testimony, Tillerson also raised the possibility of imposing sanctions on the whole of the Islamic Revolutionary Guard Corps, Iran's main military force and a major player in the country's economy.

Currently, Washington has only blacklisted the Guards' foreign operations arm - the Quds Force - and some individual commanders.

"We continually review the merits, both from the standpoint of diplomatic but also international consequences, of designating the Iranian Revolutionary Guard in its entirety as a terrorist organisation," Tillerson said.

The Guards have played a major role in training Shia fighters in Iraq that are a significant force in the fightback against the Islamic State of Iraq and the Levant (ISIL) group, and have also trained thousands of "volunteers" to battle alongside President Bashar al-Assad's forces in Syria.

The United States has had no diplomatic relations with Iran since the aftermath of the Islamic revolution of 1979 and its interests are looked after by Switzerland.

Source: AFP news agency