SEOUL, South Korea (AP) — The Latest on Secretary of State Rex Tillerson's visit to Asia (all times local):

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6:15 p.m.

Secretary of State Rex Tillerson says it may be necessary to take pre-emptive military action against North Korea if the threat from its weapons program reaches a level "that we believe requires action."

Tillerson spoke at a news conference in Seoul after visiting the heavily militarized border with North Korea on Friday.

Asked about the possibility of using military force against the North, Tillerson said, "all of the options are on the table."

He said the U.S. does not want a military conflict, but if North Korea takes actions that threaten South Korean or U.S. forces it would be met with an "appropriate response."

Past U.S. administrations have considered military force because of North Korea's development of nuclear weapons, but rarely has that option been expressed so explicitly.

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4:25 p.m.

U.S. Secretary of State Rex Tillerson visited the world's most heavily armed border, greeting U.S. soldiers on guard near the tense buffer zone between rivals North and South Korea.

Tillerson touched down by helicopter Friday at Camp Bonifas, a U.S. base about 400 meters (438 yards) from the Demilitarized Zone, a Cold War vestige created after the Korean War ended in 1953. He planned to then move to the truce village of Panmunjom inside the DMZ, a cluster of blue huts where the Korean War armistice was signed.

Tillerson is the latest in a parade of senior U.S. officials to have their photos taken at the border. But it's the first trip by the new Trump administration's senior diplomat as he makes a tour of Japan, South Korea and China.

Speaking in Tokyo, Tillerson earlier vowed a tougher strategy to confront North Korea's nuclear threat. But he offered no details about what would comprise the "different approach" to North Korea the U.S. will pursue. He pointedly noted that 20 years of "diplomatic and other efforts" had failed to dissuade the isolated communist government from developing its nuclear program, which he called an "ever-escalating threat."