A new U.S. policy toward North Korea under the administration of President Joe Biden builds on a June 2018 agreement between his predecessor Donald Trump and North Korean leader Kim Jong Un, as well as other accords, diplomatic sources said Thursday.

Japan and South Korea, two key U.S. allies in East Asia, have already been briefed on the status within the Biden administration of the agreement, in which the North committed to work toward complete denuclearization of the Korean Peninsula, the sources said.

North Korean leader Kim Jong Un and U.S. President Donald Trump at the demilitarized zone (DMZ) separating the South and North Korea on June 30, 2019. (KCNA/Kyodo)

The administration, which was launched in January, has just completed its months-long policy review on North Korea. It plans to provide humanitarian assistance to North Korea, including coronavirus vaccines, if the North so requests, according to the sources.

A U.S. diplomatic source said the "ball is in North Korea's court." It is unclear, however, whether the stalled talks on North Korea's denuclearization would resume anytime soon given Kim has made clear that Pyongyang will seek to boost its nuclear and missile capabilities.

The U.S.-North Korea joint statement was signed by Trump and Kim at their talks in Singapore on June 12, 2018. In the document, they said the United States would provide security guarantees to North Korea in return for "complete" denuclearization of the peninsula.

After the first-ever summit between the two countries, Trump and Kim met again in Vietnam in February 2019, but their talks fell short of bridging the gap between demands by the United States and North Korea's calls for sanctions relief.

The two met for a third time in June that year at the Demilitarized Zone dividing the two Koreas and agreed to restart denuclearization talks. But bilateral negotiations have stalled, with a working-level meeting held in the Swedish capital Stockholm in October that year ending without progress.

Under its new North Korea policy, the Biden administration will respect the joint statement as an international agreement in a bid to resume the stalled bilateral talks.

U.S. President Joe Biden speaks at the White House in Washington on March 12, 2021. (UPI/Kyodo)

One of the diplomatic sources said the U.S. government has explained to its allies that the new approach "will build on Singapore and other agreements made by previous administrations."

Humanitarian assistance would be considered separately from denuclearization talks. The idea of helping North Korea with coronavirus vaccines stems in part from the recognition that no substantive negotiations are likely as long as North Korea continues to keep its borders shut to fight the pandemic.

Japan, for its part, has urged the United States not to renege on the joint statement issued under the previous administration. "If (the United States) decides to begin all over again on the grounds that there was a change of government, North Korea would lose its motivation to negotiate," a high-level Foreign Ministry official said earlier.

As a presidential candidate, Biden criticized Trump, saying the then president had "legitimized North Korea" by repeatedly engaging with Kim.

The Biden administration's policy review ended last month.

The administration considered making "complete denuclearization of North Korea" its ultimate goal to make clear who is subject to denuclearization and to what extent denuclearization should be achieved. But in the end, it settled on "complete denuclearization of the Korean Peninsula," which was included in the Singapore statement, according to the sources.

"I hope that North Korea will take the opportunity to engage diplomatically and to see if there are ways to move forward toward the objective of complete denuclearization of the Korean Peninsula," Secretary of State Antony Blinken said at a joint press conference with his British counterpart Dominic Raab in London on May 3.

"We have, I think, a clear, a very clear policy that centers on diplomacy. And it is I think up to North Korea to decide whether it wants to engage or not on that basis," he added.

The U.S. government sounded out North Korea this month about making contact to brief the country on its new policy, and Pyongyang responded to it, according to the sources.

When the United States sounded out North Korea in February about possible contact, the North made no response at all, the sources said.