Iran continued to arrest opposition members on Tuesday in what seemed to be an effort to curb further protests after Sunday’s defiant demonstrations against the government, according to opposition Web sites.

The authorities arrested dozens of journalists, students and activists on Monday and Tuesday, the Web sites said. Among those arrested was the sister of the Nobel laureate Shirin Ebadi, who has been critical of the government.

The crackdown appears to be the largest since June, when antigovernment protests exploded after the country’s widely disputed presidential election.

Sunday’s protests were the bloodiest since the summer, and on Tuesday an opposition Web site, Jaras, said the death toll was likely to be significantly higher than previously thought. The site quoted what it said was a leaked confidential report by the official news agency IRNA, saying that 37 people had been killed.