North Korea is expanding a weapons plant that manufactures missiles used by Russia against Ukraine, according to new research from a US-based think tank.

The facility produces both KN-23 missiles (Hwasong-11A) and KN-24 missiles (Hwasong-11B), according to researchers at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies.

Located in the country’s second-largest city, Hamhung, the factory has been visited several times by North Korean leader Kim Jong Un, with North Korean state media previously touting its mass-production of tactical missiles.

Ukraine has been hit by a recent surge in Russian ballistic missile attacks, about a third of which used North Korean weapons, according to Ukrainian military officials.

Moscow and Pyongyang have also deepened their military ties to a level unseen since the Cold War, including agreeing to a mutual defense pact earlier this year and sending North Korean troops to help fight against Ukraine according to Western and South Korean officials.

Now, new satellite images indicate North Korea is expanding the Hamhung facility and building what appears to be a second building for the final assembly of missiles, as well as additional housing for workers.

“It seems like this is an attempt to increase the throughput on that production line that they’ve established,” Sam Lair, a research associate at the Center for Nonproliferation Studies, told CNN.

Lair said researchers have seen a lot of expansion at the facility, which is called the ‘February 11 plant’ by North Korean authorities, in the last few years alone. The size of the plant started to increase in 2020, and it has since undergone routine improvements like repairing old buildings and replacing roofs, he said.

But the new building, likely intended for missile assembly, indicates “that they’re not just improving an element of the production line, but rather, they’re trying to expand it.”

North Korea also appears to be scaling up the size of the workforce at the facility, Lair told CNN, based on his analysis of the images taken in October by satellite firm Planet Labs.

“Just outside the security perimeter of the factory, we see what appear to be new apartment buildings going up,” he said. “We can see the foundations in satellite imagery.”

The new missile assembly building is roughly 60% to 70% as large as the original building, Lair estimates.

State media footage from KCNA shows Kim Jong Un touring the plant in August 2023, showing off tail kits being added to Hwasong-11 class missiles, nozzles being fitted and nose cones capping off the short-range ballistic missiles, according to researchers. But that footage has since been removed from state media websites.

The factory is part of the Ryongsong Machine Complex, which also manufactures goods like multiple rocket launcher shells for the North Korean military, Lair said.

Attacks on Ukraine with KN-23 missiles

Russia has fired about 60 North Korean KN-23 missiles (Hwasong-11A) at Ukraine this year.

And strikes using North Korean missiles have killed at least 28 people and injured 213 this year, the Ukrainian prosecutor general told CNN last week.

CNN has previously reported on the apparent extent of US- and European-made or designed circuitry in the guidance systems of KN-23 missiles, which North Korea obtains despite sanctions.

Crucial components used in the missiles are produced by nine Western manufacturers, including companies based in the United States, the Netherlands and the United Kingdom, according to a recent report by Ukraine’s Independent Anti-Corruption Commission (NAKO), a civil society organization.

Moscow and Pyongyang have both previously denied that North Korea has exported weapons to Russia, despite significant evidence of such transfers. Meanwhile, observers have raised concerns that Moscow may be violating international sanctions to aid Pyongyang’s development of its military satellite program.

In June, the two autocratic nations signed a new landmark defense pact, pledging to use all available means to provide immediate military assistance in the event the other is attacked.

Western officials have also warned that thousands of North Korean troops have joined Moscow’s forces in its attempt to seize back the Kursk region that was taken by Kyiv’s military in a surprise offensive earlier this year.