Iran's key opposition leader said Thursday for the first time that he is being isolated by authorities and pressured to drop his presidential election challenge, while the declared winner of the vote, hardline President Mahmoud Ahmadinejad, sharply criticized US President Barack Obama. In another sign of the widening post-election crackdown, 70 university professors were arrested late Wednesday, after a meeting with Mir Hossein Mousavi, who has alleged massive fraud in the June 12 vote. The detention of the professors signaled that the authorities are increasingly targeting Iran's elite. Hundreds of protesters and activists are believed to have been taken into custody since the June 12 vote, in which Iran's ruling clerics declared hard-line President Mahmoud Ahmadinejad the winner by a landslide. Ahmadinejad dismissed growing Western criticism of the post-election clampdown, singling out President Barack Obama. "Why has Mr. Obama, who advocates change, been trapped and follows the same path as Bush," state TV quoted Ahmadinejad as saying. Before the election, the Obama administration had indicated that it was interested in reaching out to Iran, after years of a diplomatic freeze following the 1979 Islamic Revolution. Iran has given no clear signal that it is interested in Obama's overture, and in the wake of the election, the US leader has slowly ratcheted up his criticism of Iran. However, there was also indications that the disputed election has caused a rift among former Ahmadinejad supporters. Several Teheran newspapers reported Thursday that only 105 out of 290 members of parliament attended a victory celebration held by Ahmadinejad on Tuesday. Among the no-shows was Parliament Speaker Ali Larijani. In recent days, demonstrators challenging the election results have found themselves increasingly struggling under a blanket crackdown by government authorities. In a statement on his official Web site, Kalemeh, Mousavi for the first time discussed what he described as his growing difficulties. He complained of "recent pressures" on him to withdraw his election challenge and said that his access to people has been "completely restricted." Mousavi also said that because of his growing isolation, verbal attacks on him have increased, including claims that he was associating with foreigners, a particularly touchy issue in Iran where the government has been alleging foreign interference with the election. The opposition leader suggested he would stand strong. "I cannot modify black as white and white as black," he was quoted as saying. "This is not the solution to expect me to express something in which I don't believe." On Wednesday, Mousavi met with 70 university professors, said the Web site, Kalemeh. The professors, among a group pushing for a more liberal form of government, were detained after the meeting, the site said. It was not clear where they were taken, the report said. Meanwhile, another opposition leader, Mahdi Karroubi, has put off a march of mourning for at least 17 people killed in post-election protests. The march had initially been set for Thursday, but has been postponed for at least a week, according to a Web site linked to Karroubi, a reformist presidential candidate. The site said organizers had not been given permission to hold the gathering. On Wednesday, large contingents of Iranian security personnel brandished clubs, fired shots into the air and used tear gas to force back hundreds of people who, defying the regime's calls for a halt to protests, gathered outside parliament. Armored vehicles moved in to arrest the demonstrators, "shoving them in like livestock," according to a source in Teheran. Mir Hossein Mousavi, the defeated presidential candidate who says the June 12 vote was rigged, has not been seen since last Thursday and is widely believed to be in hiding. But the protests were organized through his official Web site, and he has previously sent messages urging the demonstrators to continue their rallies. In a message on another site, Mousavi's wife, Zahra Rahnavard, also urged protesters to fight on. She compared the regime's crackdown to martial law.