US Defense Secretary Jim Mattis on Friday warned that a military solution to the DPRK nuclear issue would be "tragic on an unbelievable scale," saying Washington was working to find a diplomatic solution.

"So our effort is to work with the UN, work with China, work with Japan, work with South Korea to try to find a way out of this situation," Mattis told reporters at a Pentagon news conference.

The remarks came nearly one month after a joint statement by Secretary of State Rex Tillerson, Secretary of Defense Mattis, Director of National Intelligence Dan Coats said that Trump aims to use economic sanctions and diplomatic measures to pressure the DPRK to dismantle its nuclear and missile programs.

The US remained "open to negotiations" toward peaceful denuclearization of the Korean Peninsula while staying "prepared to defend ourselves and our allies", according to the statement.