Robert Worth and Nazili Fathi of the New York Times write:





The developments followed a weekend of growing tension. On Sunday, word spread that more than 100 prominent opposition members had been detained; riots erupted in Tehran and other cities; and the triumphant incumbent hinted that his top challenger risks punishment for questioning the result.



At the same time, two of the three opposition candidates and a clerical group issued fresh statements requesting an annulment of Friday's ballot, which gave a lopsided victory to Mr. Ahmadinejad, a conservative who has become a polarizing figure at home and abroad. It was unclear how much further Mr. Ahmadinejad's adversaries were willing or able to go in challenging the result. But supporters of the opposition candidates skirmished with baton-wielding riot police officers on the edges of a government-organized victory rally in Tehran. There were also reports of riots in other Iranian cities, and the protests were echoed by Iranians demonstrating against the election results in Washington and in several European capitals.



Mr. Ahmadinejad dismissed the opposition's allegations of fraud, saying that the victory had given him a bigger mandate than ever. He criticized Mr. Moussavi, the main opposition candidate - who remained at home on Sunday with security forces closely monitoring his movements - in a veiled statement that many here saw as a threat.



"He ran a red light, and he got a traffic ticket," Mr. Ahmadinejad said of his rival during a news conference at the presidential palace.

