Dallas police in new security lockdown over anonymous threat against officers

Mourners continued to gather at a makeshift memorial outside Dallas Police headquarters on Saturday ((Getty Images))

Dallas police say they are "taking seriously" an anonymous threat to law enforcement across the city, amid high tensions two days after five of the city's officers were killed by a gunman during a protest over police shootings of black men.

An apparent lockdown of the area around police headquarters began a little after 4pm as police set up a roadblock perimeter of several blocks surrounding the building in downtown Dallas.

Police said in a statement that they had “received an anonymous threat against law enforcement across the city and… taken precautionary measures to heightened security.”

Media were ordered away from the plaza in front of the police department building, where a makeshift memorial has been swelling with flowers and other tributes since the shootings on Thursday night.

According to the department’s official Twitter account, SWAT officers “searched the police parking garage for a suspicious person.” Officers set off a small device to break through a locked fence and used a shotgun to breach a closed door in the garage. The search was completed without any suspect being found.

There had been unconfirmed reports of a man wearing a black mask spotted in the car-park behind the building, while local TV station WFAA reported that the threat had come from an armed group based Houston. The department also took a city-wide roll call of its officers to ensure they were all safe.

The incident may simply represent an abundance of caution in a city that remains on edge less than 48 hours after the deadliest day for US law enforcement since 9/11. Senior officers met at police headquarters earlier in the afternoon to discuss the ongoing investigation into the shootings, as detectives tried to determine whether gunman Micah Johnson had acted alone or had co-conspirators.

Mr Johnson was killed with explosives carried by a robot after being cornered in a downtown car-park in the early hours of Friday. Police attempts to negotiate with the suspect had failed, after his attack left five officers dead and a further seven wounded.

Two civilians were also injured after taking part in the demonstration over two recent police shootings of black men in Louisiana and Minnesota.