A Pakistani cleric has offered a 1.5 million rupee (£19,400) reward and a car for anyone who kills the cartoonist who drew the Prophet Muhammad cartoons.
Another Islamist leader has been put under house detention, amid fears of more deadly demonstrations, officials said.
The cleric did not name the cartoonist.
Several cartoonists submitted images to the Danish newspaper Jyllands-Posten, which first published them.
Meanwhile, police arrested 125 prophet cartoons protesters for violating a ban on rallies in eastern Pakistan, amid expectations of more demonstrations around the country in the wake of riots that have killed five people this week.
About 300 police swooped down on the protesters, who gathered at a roundabout in Multan city, chanting, “We are slaves of the prophet,” and trampling on a Danish flag, said Sharif Zafar, a police official in Multan.
Protesters shouted “Death to Musharraf” as they were bundled into two police buses.
Zafar said they were being taken to a police station because they were violating a ban on rallies in the Punjab province – declared after deadly riots in the provincial capital Lahore on Tuesday.
In Karachi, a youth group called Pasban called a strike in the teeming port city, where about 40,000 people joined a peaceful protest. “We expect that people of all sects and walks of life will keep their businesses shut to convey a message to the Western world,” said Altaf Shakoor, Pasban’s chief.
Supporters of the radical Jamaat-e-Islami, Pakistan’s largest Islamic group, also planned to hold rallies in Karachi after midday prayers, said Sarfaraz Ahmed, a spokesman for the anti-US. group.