Four police officers were fatally shot and seven wounded by snipers in Dallas, authorities said, during one of many demonstrations held in cities across the United States against the second fatal police shooting of a black man in two days.

Dallas Police Chief David Brown said in a statement two snipers in elevated positions shot 11 officers, killing three. Police said on Twitter later a fourth officer had died. At least one more was in surgery.

Brown also said later one suspect was cornered