TEHRAN, Iran — Iranian security forces stormed a series of opposition offices today, rounding up at least seven prominent anti-government activists in a new crackdown against the country's reformist movement, opposition Web sites and activists reported.

The arrests came a day after at least eight protesters were killed during anti-government marches marking Shiite Islam's most important observance. The bloodshed drew an especially harsh condemnation from one opposition leader, who compared the government to the brutal regime that was ousted by the Islamic Revolution three decades ago.

The reform movement has shown resilience in the face of crackdowns since June's disputed presidential election.