WASHINGTON (Reuters) - A North Korean envoy arrived in Washington on Thursday for expected talks with Secretary of State Mike Pompeo and a possible encounter with President Donald Trump aimed a laying the groundwork for a second U.S.-North Korea summit.

The envoy arrived on the same day Trump unveiled a revamped U.S. missile defense strategy that singled out North Korea as an ongoing and “extraordinary threat,” seven months after he declared after his first summit with leader Kim Jong Un that the North Korean threat had been eliminated.

Kim Yong Chol, Pyongyang’s lead negotiator in denuclearization talks with the United States, was due to meet Pompeo and could also go to the White House on Friday, a person familiar with the plan said, a sign of potential movement in a diplomatic effort that has appeared stalled for months.

The North Korean visit could yield an announcement of plans for another summit between Trump and Kim Jong Un, the source said, speaking on condition of anonymity.

There has been no indication, however, of any narrowing of differences over U.S. demands that North Korea abandon a nuclear weapons program that threatens the United States or Pyongyang’s demand for a lifting of punishing sanctions.

Kim Yong Chol, a hardline former spy chief, arrived in Washington on a commercial flight from Beijing, South Korea’s Yonhap news agency reported. Yonhap and other South Korean media said he was greeted at Dulles airport by Stephen Biegun, the U.S. special representative for North Korea.

Pompeo had planned to meet his North Korean counterpart to discuss a second summit last November, but the meeting was postponed at the last moment.

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Diplomatic contact was resumed after Kim Jong Un delivered a New Year speech in which he said he was willing to meet Trump “at any time,” South Korea’s ambassador to the United States, Cho Yoon-je, told reporters last week.

Kim Yong Chol was last in Washington in June, when he delivered a letter from Kim Jong Un to Trump that opened the way for the June 12 summit in Singapore.

That meeting yielded a pledge from the latter to work toward denuclearization of the Korean peninsula and Trump declared the next day that there was “no longer a nuclear threat from North Korea.”

There has been little obvious progress since, however, which was underlined by the Missile Defense Review unveiled on Thursday.

Introducing the report, acting U.S. Defense Secretary Patrick Shanahan noted that North Korean missiles remained a “significant concern.” Trump himself only mentioned North Korea in passing at the same event, saying negotiations he had conducted should have been done years ago.

“CONCRETE STEPS”

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U.S. Vice President Mike Pence acknowledged on Wednesday that efforts to persuade North Korea to give up its nuclear arsenal had not made headway.

“While the president is promising dialogue with Chairman Kim, we still await concrete steps by North Korea to dismantle the nuclear weapons that threaten our people and our allies in the region,” Pence said in an address to U.S. ambassadors and other senior American diplomats at the State Department.

Trump said on Jan. 2 that he had received a “great” letter from Kim Jong Un and would probably meet him again in the not-too-distant future, but there was no rush.

Pyongyang had stopped missile and bomb testing and if it had not been for his administration “you’d be having a nice big fat war in Asia,” he said.

CNN quoted a source familiar with the U.S.-North Korea talks as saying that Kim Yong Chol would be carrying a new letter from Kim Jong Un to Trump.

Kim Yong Chol will be the first top North Korean official to stay overnight in Washington since the late Vice Marshal Jo Myong Rok did so ahead of talks with then-President Bill Clinton and Secretary of State Madeleine Albright in 2000.

Communist-ruled Vietnam, which has good relations with both the United States and North Korea, has been widely touted as the most likely venue for a second meeting between Trump and Kim Jong Un.

The Washington Post quoted people familiar with recent diplomatic activity as saying that if announced soon, the summit would probably take place in March or April, with the coastal city of Danang the most likely venue.