U.S. imposing more sanctions against N.Korea soon: White House

"We're going to add additional sanctions very shortly that will continue to put that maximum pressure on North Korea," White House spokeswoman Sarah Sanders told Fox News in an interview.

Sanders also said the administration would also "try to push Russia to take a bigger and bolder stance to put more pressure on North Korea."

(Reporting by Susan HeaveyEditing by Chizu Nomiyama)