(CNN) -- U.S. Defense Secretary Robert Gates on Friday urged North Korea to end its belligerent acts and take concrete steps to meet expectations of the international community.
Gates was in Seoul, South Korea, the final stop of a five-day trip to Asia that included China and Japan.
The theme of the trip was to ensure peace and stability on the Korean Peninsula, he said.
"The DPRK leadership must stop these dangerous provocations and take concrete steps to show they will begin meeting their international obligations," Gates said at an open session with his South Korean counterpart, Kim Kwan-jin.
"With regard to next steps on North Korea, diplomatic engagement is possible, starting with direct engagement between DPRK and the South."
DPRK refers to the Democratic People's Republic of Korea, the official name of North Korea.
The secretary said negotiations are still a viable option.
"When or if North Korea's actions show cause to believe that negotiations can be productive and conducted in good faith, then we could see a return to the six-party talks," Gates said.
During his trip, the secretary expressed concern about Pyongyang's military ambitions, saying that it had grown more "lethal" and "destabilizing," not only for the Korean Peninsula but also for the Pacific Rim and the international community.
Tensions between the Koreas escalated after the North's shelling of the South's Yeonpyeong Island in November, as well as the March sinking of a South Korean warship -- allegedly by a North Korean torpedo -- and recent revelations that it is enriching uranium for nuclear weapons.
North Korea has denied sinking the warship.
Seoul has taken a tough stance against the North with strong rhetoric.
Washington has been concerned about North Korea's efforts to develop its nuclear program. The United States, along with North Korea, South Korea, Russia, Japan and China, are part of the six-party talks.