WASHINGTON/SEOUL, Nov 25 (Reuters) - North Korea is expanding a key weapons manufacturing complex that assembles a type of short-range missile used by Russia in Ukraine, researchers at a U.S.-based think tank have concluded, based on satellite images.

The facility, known as the February 11 plant, is part of the Ryongsong Machine Complex in Hamhung, North Korea’s second-largest city, on the country’s east coast.

Sam Lair, a research associate at the James Martin Center for Nonproliferation Studies (CNS), located at the Middlebury Institute of International Studies at Monterey, said the plant was the only one known to produce the Hwasong-11 class of solid-fuel ballistic missiles. Ukrainian officials say these munitions - known as the KN-23 in the West - have been used by Russian forces in their assault on Ukraine. The expansion of the complex has not been previously reported.

Both Moscow and Pyongyang have denied that North Korea has transferred weapons for Russia to use against Ukraine, which it invaded in February 2022. Russia and North Korea signed a mutual defense treaty at a summit in June and have pledged to boost their military ties. North Korea’s mission to the United Nations did not respond to a request for comment for this story.

The satellite images, taken in early October by the commercial satellite firm Planet Labs, show what appears to be an additional assembly building under construction as well as a new housing facility, likely intended for workers, according to the analysis by researchers at CNS.