US Vice President Mike Pence visited the Korean Demilitarized Zone and the border town of Panmunjom, where he said the "era of strategic patience" with North Korea is over.
Pence said on April 17 that Washington wants to act on this issue "through peaceful actions and negotiations".
"But all options are on the table as we continue to stand side by side with the South Korean people," Pence said during his visit to the village of Panmunjom.
Speaking from Freedom House, a few meters from the military demarcation line, Pence said that "the people of North Korea, the North Korean military, should not be mistaken for the determination of the US to stand by its allies."
Pence's visit to the border between South and North Korea comes as tensions on the peninsula have risen over Pyongyang's nuclear program.
A day earlier, the North failed to launch a missile, which exploded almost immediately after launch.
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Pence: USA and South Korea - unique in policy towards North Korea
US Vice President Pence is on his ten-day tour of Asia.
He will visit key ally Japan, which has also condemned North Korea's nuclear program.
Later today, Pence is expected to meet with South Korea's acting president, Hwang Kyo-ahn.
