CAIRO, Aug 15 (Reuters) - Three Islamist protesters were killed on Friday during clashes between police and demonstrators in Cairo, Egyptian security sources said.

The men died from bullet wounds during clashes between a few hundred protesters and police in Giza on the outskirts of the capital, the sources said.

An Interior Ministry statement said that one of the dead had been wearing a mask and carrying a weapon used for firing birdshot, petrol bombs, and grenades.

Violence has polarised Egyptians since the army overthrew the elected president, the Islamist Mohamed Mursi, last year following mass protests against his rule.

Mursi's Muslim Brotherhood, once Egypt's most organised political movement, was declared a terrorist organisation last year, and its political wing was banned last week.

Small hit-and-run demonstrations are the most that the group can muster after a fierce security crackdown.

Hundreds of Brotherhood supporters have been killed and thousands arrested since Mursi was ousted. The largest number of deaths occurring almost exactly a year ago, on Aug. 14, when security forces stormed two protest camps in Cairo.

(Reporting By Maggie Fick; Editing by John Stonestreet, Larry King)