US Defense Secretary Jim Mattis said Wednesday that a string of global security threats, including North Korea's "reckless" and "provocative" behavior, requires the United States to maintain strong nuclear and conventional forces.

"We must look reality in the eye: we see Russia and China seeking veto power over the economic, diplomatic, and security decisions of nations on their periphery. Terrorist groups murder the innocent and threaten peace in many regions and target us," Mattis said before a Senate Appropriations Committee hearing.

"North Korea's reckless rhetoric and provocative actions continue despite United Nations censure and sanctions. This situation calls for our Department to maintain a safe and secure nuclear deterrent and a decisive conventional force that can also fight irregular enemies, since our military must be able to counter all threats facing us," he said.

Mattis expressed concerns about proliferation from North Korea and Iran.

"We also see in the case of North Korea and Iran a proliferation issue, one that has been delayed in Iran, but we see the reckless behavior north of the DMZ on the Korean Peninsula as unsettling the northwestern Pacific, East Asia area," he said.

He said the US prefers diplomatic solutions, and the military has roles in ensuring the country negotiates from a position of strength and setting conditions for diplomatic progress.

Mattis also criticized China for adopting "the tribute nation kind of approach" in the region, in which "all other nations have to pay tribute or acquiescence to the more powerful nation, the larger nation." (Yonhap)