KARACHI, Pakistan — Thousands of members of radical Islamic groups have rallied in the southern city of Karachi against an anti-Islam film that has sparked violence across the Muslim world.

The film, "Innocence of Muslims," has enraged many Muslims for deprecating the Prophet Muhammad. At least 51 people, including the U.S. ambassador to Libya, have been killed in violence linked to the film, which also has renewed debate over freedom of expression in the United States and in Europe.

Chanting "Down with America," the participants gathered in the heart of the city's business district Saturday. Prominent radical leader Muneebur Rehman demanded stern punishment for the filmmaker.

Senior police officer Asif Ijaz Sheikh estimated the crowd numbered more than 15,000. He says the protesters dispersed peacefully.

A similar rally was also expected in Islamabad Saturday.