The full Minnesota National Guard was activated for the first time since World War Two after four nights of civil unrest that has spread to other US cities following the death of a black man shown on video gasping for breath as a white Minneapolis policeman knelt on his neck.

Minnesota Governor Tim Walz said the deployment was necessary because outside agitators were using protests over Monday’s death of George Floyd to sow chaos and that he expected Saturday night’s demonstrations to be the fiercest so far.

From Minneapolis to several other major cities including New York, Atlanta and Washington, protesters clashed with police late on Friday in a rising tide of anger over the treatment of minorities by law enforcement.