A crackdown on nationwide protests in Iran has killed at least 544 people and even more are feared dead, activists said Sunday, while Tehran warned that the U.S. military and Israel would be “legitimate targets” if America uses force to protect demonstrators. 

About 10,600 people have been detained over the two weeks of protests, according to the U.S.-based Human Rights Activists News Agency, which has been accurate in previous cases of unrest in Iran in recent years. The organization said of those killed, 496 of the dead were protesters and 48 were with security forces.

There are reports of protesters getting shot in the head.

With the internet shut off in Iran and phone lines down, gauging the demonstrations from abroad has grown more difficult. 

The Associated Press has been unable to independently assess the toll. 

The Iranian government has not offered overall casualty figures for the demonstrations.