Dallas police say they have heightened security at their headquarters after receiving an anonymous threat, two days after the deadly shooting in the city.
SWAT officers were deployed at the main building, in effect placing it under lockdown, local media say.
On Thursday, five white police officers were shot dead by a black man, Micah Johnson, during a protest rally.
The march was against the killing of black men by police. Two deaths this week have led to nationwide protests.
-bbc