Dallas police have given the all clear, hours after security levels were raised at their headquarters in the city.
They said they had received an anonymous threat, two days after the killing of five police officers.
A nearby parking lot was searched for a “suspicious person” but no-one was found. SWAT officers were earlier deployed at the main building.
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.
Dallas police said its officers – using dogs – searched the parking lot but the hunt turned up nothing.
In a statement earlier on Saturday, the police said: “The Dallas Police Department received an anonymous threat against law enforcement across the city and has taken precautionary measures to heighten security.”
An armoured vehicle was moved close to the main HQ in central Dallas and heavily armed officers were seen nearby, according to the Associated Press news agency.
But it added that members of the public were still able to walk about freely around the building.
The police asked media to stop all live feeds around HQ “for the safety of our officers”, the BBC’s James Cook reports.
The shooting happened late on Thursday during the protest march. Johnson, who was himself killed during the assault, supported black militant groups who encouraged violence against police.
Dallas police chief David Brown said Johnson had told a negotiator that he had wanted to kill white people, especially white police officers, because he was angry about the recent shootings of black men by police.

Source: BBC