Thousands of people from Pakistan's most powerful tribe are rallying in the capital, Islamabad, demanding the arrest of a police officer accused of killing a 27-year-old aspiring model in Karachi, the country's largest city.

Thursday's rare protest by the Mehsud tribe comes hours after a court ordered officer Rao Anwar arrested for the death of Naqeeb Ullah in a Jan. 13 shootout.

Ullah was from the Mehsud tribe and a government probe says he was innocent. Authorities have relieved Anwar of his duties.

Holding portraits of Ullah, protesters said they came to seek justice.

The protesters are from the Taliban's former stronghold of South Waziristan, which borders Afghanistan, and other nearby towns and cities.

They have threatened to hold a sit-in outside parliament if Anwar is not arrested.