DALLAS (Reuters) - Dallas police headquarters and surrounding blocks were cordoned off and SWAT teams were deployed on Saturday after authorities received an anonymous threat against officers across the city, but a search for a “suspicious person” turned up no one, officials said.

The incident occurred as the city remained tense following Thursday night’s fatal shootings of five Dallas police officers by a former U.S. Army reservist. Police asked news organizations to stop airing live video from the area as they carried out the search.

Police said on Twitter that “out of an abundance of caution, officers searched the garage to ensure reports of a suspicious person (were) thoroughly investigated.” Police said they used a shotgun to get through a locked door during the search.

Before police sounded the “all clear,” tactical officers dressed in protective gear and armed with rifles searched the three-story structure, police said.

The department said there was no formal lockdown at the headquarters despite earlier media reports characterizing the incident that way. All streets around the building, however, were barricaded and vehicles were not allowed to enter the area, a Reuters eyewitness said.

“The Dallas Police Department received an anonymous threat against law enforcement across the city and has taken precautionary measures” to heighten security, Dallas police said in an emailed statement.

Before starting the sweep of the garage, officers pushed back reporters and camera operators who had gathered outside the headquarters in the Texas city’s downtown after initial reports of the lockdown.