Kazakh prosecutors are pressing charges against a newspaper editor, an opposition leader and three policemen in connection with deadly clashes last month in a western oil town.

Kazakhstan's National Security Service on Monday arrested the editor of the weekly Vzglyad newspaper (Igor Vinyavsky), as well as Vladimir Kozlov, leader of the unregistered Alga party, on charges of fomenting unrest in the Central Asian republic.

Prosecutors have also charged three police officers with using excessive force in dealing with protesting oil workers.

The clashes, in the town of Zhanaozen, occurred on the 20th anniversary of Kazakhstan's independence from the Soviet Union, when a protest by laid off government oil workers turned violent, leaving at least 15 people dead.

Officials said the clashes erupted after some of the protesters tore down traditional yurts, or tents, that had been put up in the town's central square. But demonstrators told social media networks that they had been surrounded by police, who opened fire.