About 2,000 people including security personnel have been killed in protests in Iran, an Iranian official said on Tuesday, the first time authorities have acknowledged the high death toll from an intense crackdown on two weeks of nationwide unrest.

The Iranian official, speaking to Reuters, said that what he called terrorists were behind the deaths of both protesters and security personnel. The official did not give a breakdown of who had been killed.

The unrest, sparked by dire economic conditions, has been the biggest internal challenge to Iranian authorities for at least three years and comes amid intensifying international pressure after Israeli and U.S. strikes last year.

Iran's clerical authorities, in power since a 1979 Islamic Revolution, have tried to take a dual approach to the demonstrations, calling protests over economic problems legitimate while enforcing a harsh security crackdown. They have accused the U.S. and Israel of fomenting unrest and said unnamed people they call terrorists have hijacked the protests.

A rights group had previously identified hundreds of people killed and said that thousands had been arrested.

Communications restrictions including an internet blackout over recent days have hampered the flow of information.

Videos of nighttime clashes between demonstrators and security forces over the past week, including several that were verified by Reuters, have shown violent confrontations with gunfire and burning cars and buildings.