5 police officers have been killed by sniper fire in Dallas, following protests against a spate of shootings by US police of black men.
6 other police officers were wounded in the attacks.
Three people have been arrested and police have been involved in a standoff with a further armed man.
Dallas police say they believe the suspects were working together to attack officers while the demonstration was underway.
Protests were taking place after the deaths of Philando Castile in Minnesota and Alton Sterling in Louisiana.
Dallas Police Chief David Brown says the suspect involved in the standoff has warned there may be bombs placed in several locations in the city.
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