Satellite images show renewed activity at a North Korean nuclear facility, suggesting that Kim Jong Un's regime is preparing to start or has already started reprocessing plutonium for nuclear weapons, experts say.

The commercial satellite photos show steam or smoke rising from a small building at the Yongbyon Radiochemistry Laboratory and from an adjacent thermal plant. The lab reprocesses spent fuel rods to extract plutonium for nuclear bombs.

The photos, released by Maxar Technologies and the Center for Strategic and International Studies, were posted on the think tank's website, Beyond Parallel.

Previous satellite imagery had shown other signs of activity at the thermal power plant in recent weeks. The head of the International Atomic Energy Agency, Rafael Mariano Grossi, this month cited signs of activity at the Yongbyon facility and another site, calling the nuclear work a clear violation of U.N. sanctions.

The latest activity suggests that North Korea has launched is preparing to launch a new effort for nuclear reprocessing, said Victor Cha, Korea chair at the Center for Strategic and International Studies, who was a senior national security official in the George W. Bush administration.

The move and two rounds of missile tests in recent weeks are a political maneuver by Kim to challenge President Joe Biden's administration and South Korean President Moon Jae-in, Cha said.

"It is a series of escalations. I think it's pretty calculated. They're ratcheting up pressure as they had done to President Trump and to President Obama," Cha said.

The moves are "nothing new with regard to North Korea, but this is happening fairly early on in the administration," he said.

The White House, the State Department and the Defense Department did not immediately respond to requests for comment.

After the Biden administration presented a united front with allies in Asia, including Japan and South Korea, and took a tough line in talks with China, "I think North Korea feels like it has to respond," said Cha, who is also a professor of government at Georgetown University.

To further escalate, North Korea could fire off longer-range missiles, conduct a nuclear test or launch an intercontinental ballistic missile, possibly from a submarine, Cha and other experts said.

North Korea has not conducted an intercontinental ballistic missile test since late 2017. After a period of high tensions, the Trump administration pursued diplomacy with Pyongyang. Talks between Trump and Kim in Hanoi, Vietnam, in 2019 ultimately collapsed with no agreement.

The U.N. Security Council held a closed-door meeting about North Korea on Tuesday, but the discussions produced no immediate outcome. The U.S. ambassador to the U.N., Linda Thomas-Greenfield, said Monday that "we're looking at additional actions that we might take here in New York."

North Korea has made a string of provocative moves and statements in recent weeks.

As the U.S. and South Korea carried out computer-simulated joint military exercises, Kim Yo Jong, the sister of North Korea's leader, warned Washington on March 16 against "causing a stink."

Days later, North Korea launched a pair of short-range cruise missiles into the Yellow Sea. Senior Biden administration officials said at the time that the cruise missile tests were at the low end of the scale in terms of what the regime could do to raise tensions.

Then, last week, North Korea fired two short-range ballistic missiles in violation of U.N. resolutions. Kim's sister on Friday called South Korean President Moon "a parrot raised by America."

At his first news conference last week, Biden said the U.S. would consult with its allies and respond if the regime chose "to escalate."

White House press secretary Jen Psaki said Monday that Biden had no plans to meet with Kim.

"I think his approach would be quite different, and that is not his intention," Psaki said.

Rear Adm. Michael Studeman, director of intelligence for U.S. Indo-Pacific Command, said this month that recent North Korean nuclear activity could be designed to gain leverage with the U.S. to try to secure relief from punishing sanctions.

"We have our eye on this. And it is deeply concerning where North Korea wants to go," Studeman said at a virtual event. If North Korea has started reprocessing, "then that could put us into a different level of tension with Korea going into 2021," he said. (NBC News)

Update news