Investigators have determined that the shooter in Dallas who killed five police officers did not have any connection to terrorist organisations, the White House has said.

"It is my understanding that investigators have now publicly ruled out the possibility that the individual who carried out this terrible act of violence had any sort of connections to terrorist organisations either in the United States or around the world," White House spokesman Josh Earnest told reporters in Warsaw, where President Barack Obama had attended a NATO summit.

"I don't think that there's a link to any sort of terrorist conspiracy," Earnest said.