SEOUL, South Korea — The United States is ready to restart nuclear negotiations with North Korea, a senior U.S. diplomat said Wednesday, a day after U.S. and South Korean militaries ended their regular drills that North Korea calls an invasion rehearsal.

During the 10-day U.S.-South Korean training, largely computer-simulated war games, North Korea raised tensions with its own missile and other weapons tests. But North Korea’s typical harsh rhetoric over the drills focused on South Korea, not the United States, in a suggestion that it’s still interested in resuming nuclear talks with the U.S.

President Donald Trump said recently he received a “beautiful” three-page letter from North Korean leader Kim Jong Un. Trump said Kim wanted to meet again to restart the talks after the U.S.-South Korean drills ended and that Kim offered him “a small apology” over the weapons tests.

North Korea’s Kim expresses ‘great satisfaction’ over weapons tests The launches were North Korea's sixth round of tests since late July, revealing a new rocket artillery system and two short-range mobile ballistic missile systems that could strike targets throughout South Korea, including U.S. bases there.

On Wednesday, Trump’s top envoy on North Korea, Stephen Biegun, told reporters in Seoul that “we are prepared to engage as soon as we hear from our counterparts in North Korea.”

Biegun said that Trump assigned his team to restart working-level talks with North Korea, in line with what Trump and Kim agreed during their third summit in late June. “I am fully committed to this important mission and we will get this done,” Beigun said.

Beigun also denied media speculation that he may be appointed as the new U.S. ambassador in Russia. “I will remain focused on making progress on North Korea,” he said.

Beigun was in Seoul for talks with South Korea. His South Korean counterpart Lee Do-hoon said the two discussed how to quickly resume the nuclear negotiations and produce “substantial progress.”

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U.S.-led diplomacy on how to rid North Korea of its nuclear weapons collapsed after Trump rejected Kim's demand for sweeping sanctions relief in return for partial disarmament steps during their second summit in Vietnam in February. During their third meeting at the Korean border village of Panmunjom on June 30, the two leaders agreed to restart the talks but there has been no public meeting between the countries.

Many experts say North Korea’s recent weapons tests were mainly aimed at applying pressure on the United States ahead of a possible resumption of talks, while registering its protest against the military drills. Most of the weapons tested were short-range missiles and rockets that experts said could target South Korea, not the mainland U.S.