Shirin Ebadi, Iran's Nobel peace laureate, has said her country faces a catastrophe that could undermine security in the whole region if government repression of the people is not stopped.

"A recurrence of the recent months' events, the continuation of the repressive policies and the killing of defenceless people could bring about a catastrophe that may undermine peace and security in Iran, if not in the entire region," Ebadi said in an open letter to the United Nations on Wednesday.

The office of Navi Pillay, the high commissioner for human rights, confirmed she had received the letter, which comes as the 47-member council prepares to hold a three-hour review of Iran's human rights policies on February 15.

Saying the patience and tolerance of Iranians was not limitless, Ebadi urged action to persuade the government to change course, calling on the council to appoint a special investigator for Iran who could help end mounting repression.

The letter comes on the eve of the 31st anniversary of Iran's Islamic revolution.

Opposition activists have called for anti-government protests on Thursday but the authorities have pledged to crack down hard if they take place.

Earlier the government announced the arrest of several people it said were preparing to disrupt official rallies.

Widespread unrest erupted in the wake of the disputed presidential vote in June last year, amid allegations that the election, resulting in Mahmoud Ahmadinejad winning a second term, was rigged.