Amnesty International has called on the Yemeni authorities to investigate the killing of a prominent southern activist after his group accused the police of targeting him during a peaceful protest.

Khalid al-Junaidi, 42, was shot dead in his car Monday as he was documenting the response to calls for civil disobedience in the southern city of Aden. Protesters in Aden have been camped out in the streets since October demanding the south separate from the north after a union formed in 1990 failed to address the region's problems. Al-Junaidi was released from prison last month after he was accused of being behind the unrest in the south.

The police declined comment on al-Junaidi's killing. Amnesty in a statement late Monday called the killing "deliberate" and an "extrajudicial execution."