Editor's note: Iranian authorities have barred journalists for international news organizations from reporting on the streets and ordered them to stay in their offices. This report is based on the accounts of witnesses reached in Iran and official statements carried on Iranian media.

Iranian authorities briefly arrested dozens of university professors who met with embattled opposition leader Mir Hossein Mousavi, his Web site said Thursday, but he vowed to persevere with his election challenge despite the apparent attempt to isolate him from his supporters.

The declared winner of the June 12 balloting, hard-line President Mahmoud Ahmadinejad, accused President Barack Obama of meddling in Iran's affairs.

Obama, along with other Western leaders, has ratcheted up his criticism of Iran's clampdown on postelection protesters in recent days, which Tehran has described as foreign interference.

In the latest sign of government attempts to silence dissent, 70 professors were detained late Wednesday after meeting with Mousavi, who has alleged massive fraud in the balloting. They were among a group pushing for a more liberal form of government, and all but four were released, his Web site said later. The four still in custody included Qorban Behzadiannejad, Mousavi's former campaign manager.

Since Saturday, demonstrators challenging the election results have found themselves increasingly struggling under a blanket crackdown by government authorities.

State media reported Thursday that in addition to the 17 protesters killed in the recent unrest, eight members of the pro-government Basij militia were killed and dozens more wounded by weapons and knives. The reports could not be independently verified.

A Thursday march by another opposition figure, reformist presidential candidate Mahdi Karroubi, was postponed for lack of a permit, a day after club-wielding security forces dispersed a small group of protesters outside Iran's parliament.

Mousavi's Web site, Kalemeh, said he has applied for permission to hold a gathering to commemorate the "martyrs" of the postelection campaign. The statement did not elaborate or give a date.

Mousavi, who last led a massive protest rally a week ago, described his growing difficulties for the first time in a statement on the site.

He said authorities were increasingly isolating and vilifying him to try to get him to withdraw his election challenge, but Mousavi added he would not back down.