U.S. Secretary of Defense Chuck Hagel made a symbolic visit to the heavily armed truce village bordering North Korea on Monday, stressing its strategic importance in defending the Korean Peninsula.

Hagel made the Demilitarized Zone tour his first order of an unprecedentedly long, four-day visit to the Asian ally ahead of an annual bilateral defense summit slated for Wednesday, which is expected to assess the North Korean threat and alliance issues with Seoul.

Hagel shook hands with soldiers and spoke briefly outside the dining hall at a U.S. military camp near the 4-kilometer wide zone inside the truce village of Panmunjom, then walked into the heavily patrolled no-man's land to tour a small post. It's where South Korean forces patrol about 25 meters from the military demarcation line.

The Pentagon chief and his South Korean counterpart, Kim Kwan-jin, looked across the line that has bisected the Korean Peninsula for the last six decades.

He spent about 20 minutes at an observation post, looking first toward North Korea, then back to the South.

"This is a very important location for our relations, and probably there is a clear identification of the ROK-US partnership here more than anywhere else," Hagel told reporters, referring to South Korea's official name Republic of Korea. "This is obviously a critical area that assures our joint vigilance for the security and safety of South Korea."

It was an unmistakable show of force to communist North Korea and its young leader who continues to advance his country's weapons program.

During the tour, he paid attention to the North Korean border town of Kaesong, asking whether the joint industrial complex is now open and how businessmen get to the complex.

All operations at Kaesong were halted in early April after Pyongyang pulled out all of its 53,000 workers from the complex that is home to 123 South Korean factories amid heightened military tensions.

Work recently resumed after long drawn-out negotiations secured a pledge from the North that it will take no future action to halt operations. 

It is Hagel's first trip to South Korea since taking office in February. He is traveling together with Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff (JCS).

The main purpose of his visit is to hold the annual Security Consultative Meeting (SCM) with South Korean Defense Minister Kim Kwan-jin, where key topics will include Seoul's request for a delay in its planned regaining of the wartime operational control (OPCON) of its troops from the U.S. (Yonhap news)