The sister of Iranian Nobel Peace Prize winner Shirin Ebadi is among at least 18 people arrested in Iran as part of the regime's crackdown on the opposition, it was claimed today.

Ms Ebadi said that intelligence agents had arrested her sister, who is a professor of medicine, on Monday.

“She is not an activist and her arrest is in fact new pressure to stop my human rights work,” Ms Ebadi said in a statement carried by the Rahesabz opposition website.

The news came as Iran summoned the British ambassador in Tehran today after the regime said unrest in the country was linked to “foreign enemies”.

The British Embassy said that envoy Simon Gass would respond “robustly” to any criticism and reiterate that Iran must respect human rights as the crackdown on opposition leaders intensified.

Ramin Mehmanparast, an Iranian foreign ministry spokesman, said: “If any nation encourages the rioters, it constitutes interference in another nation’s internal affairs.”

The round-up of activists began on Sunday in an attempt to end street protests after deadly weekend clashes erupted during the Shi’ite Muslim religious ritual of Ashura. At least eight were killed on Sunday.

Among those arrested are three senior advisers to opposition leader Mirhossein Mousavi and his brother-in-law, opposition websites reported.

Ms Ebadi, who left Iran a day before the disputed June 12 poll, has been urging the international community to act against what she sees as human rights violations by the Islamic regime since the election.

She was awarded the Nobel Peace Prize in 2003 for her legal work championing human rights in Iran.

Tens of thousands of government supporters rallied across Iran today to call for the punishment of opposition leaders for fomenting unrest after June’s disputed presidential poll, state media reported.

Political turmoil has entered a new phase in Iran with bloody face-offs and arrests over the vote won by President Mahmoud Ahmadinejad, with security forces calling on the authorities to deal“firmly” with opposition leaders.

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