US police on guard after threats following Dallas sniper shootings

Police forces across the United States are on guard after receiving threats in the aftermath of the killings of two black men and the sniper attack in Dallas which left five police officers dead.

Some departments have ordered officers to pair up while others have tightened security.

The authorities have said that Dallas gunman, Micah Johnson, wanted to "exterminate" whites following the deaths of Philando Castile in Minnesota and Alton Sterling in Louisiana.

Another man who killed one person and wounded three others - including a police officer - in Tennessee reportedly told investigators he was motivated by the recent kills of black men by police.

On Saturday, Dallas Police received an anonymous threat, leading to police swarming the department's headquarters, searching for a reported suspicious person in the garage next to the building. No one was found and the all-clear was issued.

In Louisiana, a man was accused of posting a video online showing him in his vehicle behind a police car, saying he wanted to kill an officer. Authorities reported that Kermonte Gilmour flashes a handgun in the video and talks about the killings of Mr Castile and Mr Sterling.

Police say a Wisconsin man posted calls on social media for black men to gun down white officers, and a woman in Illinois is accused of threatening in an online video to shoot and kill any officer who pulled her over.

In Mississippi, Waveland Police Chief David Allen told a local newspaper threats had come via phone and social media and involved possible gunfire attacks over the weekend. Extra police were on duty.