WASHINGTON (AP) — The newly appointed U.S. special envoy for North Korea will make his first diplomatic trip abroad next week in the Trump administration's latest effort to press for progress in uncertain denuclearization talks.

As President Donald Trump expressed confidence he and North Korean leader Kim Jong Un "will get it done together" following talks between Kim and South Korean officials, the State Department announced Thursday that Stephen Biegun will visit South Korea, China and Japan between Sept. 10 and Sept. 15.

Biegun, who was named late last month as special representative for North Korea, "will meet with his counterparts and continue diplomatic efforts to achieve the final, fully verified denuclearization of North Korea as agreed to by Chairman Kim in Singapore," the department said, referring to Trump's historic June 12 summit with Kim.

He had been set to visit North Korea with Secretary of State Mike Pompeo last week, but Trump called off the trip, citing a lack of progress. That postponement put new urgency into South Korean President Moon Jae-in's attempts at rapprochement with Kim, which led to the visit to Pyongyang of some of his top aides who arranged a third summit between Moon and Kim for Sept. 18-20.

Those officials said earlier Thursday that Kim still has faith in Trump's commitment to ending their nations' hostile relations, but is frustrated by questions about his willingness to denuclearize and wants his "goodwill measures" to be met in kind. They also said they forwarded a message from Trump to Kim during their meeting and would send a separate message from Kim to Trump.

Trump responded by tweeting, "Kim Jong Un of North Korea proclaims 'unwavering faith in President Trump.' Thank you to Chairman Kim. We will get it done together!"

Despite that sentiment, there were signs that progress could remain elusive.

In a move that will irk North Korea, the U.S. Justice Department announced charges against North Korean computer programmer Park Jin Hyok in connection with several major cyberattacks, including the hack of Sony Pictures Entertainment in 2014, a February 2016 cyber-enabled fraudulent transfer of $81 million from Bangladesh Bank and the WannaCry ransomware attack in May 2017.

And, the Treasury Department hit Park and the company he worked for, Chosun Expo Joint Venture, with sanctions that will freeze any assets they may have in U.S. jurisdictions and bar Americans from doing any business with them.

"We will not allow North Korea to undermine global cybersecurity to advance its interests and generate illicit revenues in violation of our sanctions," Treasury Secretary Steven Mnuchin said in a statement. "The United States is committed to holding the regime accountable for its cyber-attacks and other crimes and destabilizing activities."

And, speaking earlier Thursday in India, Pompeo said an "enormous amount of work" remains.

He said the U.S. will continue to work with North Korea to "deliver for the world" in upholding U.N. Security Council resolutions against its nuclear and missile programs, and the commitments Kim made at the summit with Trump on denuclearization.

"It is the case that there is still an enormous amount of work to do," Pompeo told a news conference in New Delhi. "We haven't had any nuclear tests, we haven't had any missile tests, which we consider a good thing. But the work of convincing Chairman Kim to make the strategic shift that we've talked about for a brighter future for the people of North Korea continues."

Although North Korea has destroyed at least parts of its nuclear test site, and says it has dismantled a missile engine test site, it has yet to declare what is in its atomic arsenal or take concrete steps to end its weapons program. Last month, the U.N. atomic watchdog vied "grave concern" about the continuation and development of the nuclear program.