It was the first time the two sides met for formal negotiations following the collapse of February's second summit between US.

President Donald Trump and North Korean leader Kim Jong-un. But the North walked out of the talks, blaming the US for failing to come up with a new proposal.

At their meetings Tuesday, the three sides "reaffirmed the importance of continued close US-ROK, US-Japan, and trilateral coordination on North Korea to achieve complete denuclearization and bring lasting peace to the Korean Peninsula," the State Department said in a statement.

ROK stands for South Korea's official name, the Republic of Korea.

Lee spoke briefly to reporters as he left the meetings but refused to share details.

"We spoke mostly about how to keep the momentum for dialogue (with North Korea)," he said. "South Korea and the US are coordinating well and we will continue to do so."

North Korea had demanded that the US come to the table with a new proposal after the summit in Vietnam broke down over differences on how much the North should denuclearize before receiving sanctions relief from the US.

Pyongyang has also stepped up calls for US security guarantees for its regime.

Lee, the South Korean envoy, became a target of North Korean criticism Tuesday.

In an article published in the Choson Sinbo, a pro-North Korea newspaper based in Japan, the North denounced the South for trying to play a "mediating role" in denuclearization talks between Pyongyang and Washington and claimed that Seoul cannot do anything independently of Washington.

"It is dumbfounding, as what role on earth the South is trying to play at a time when it can't do anything but just pay attention to what the US says," the paper said. (Yonhap)