ABUJA, Aug 2 (Reuters) - Nigerian police are on red alert and may seek the help of the military after protests against the cost of living and governance issues turned violent in some cities, the inspector general of police said.

At least three protesters were killed in northern Kaduna state on Thursday, Reuters reporters and protesters said.

Amnesty International said on Friday at least 13 protesters in total had been killed in three northern states, but the authorities have not commented on any deaths.