More than 1,000 North Korean soldiers have been killed or wounded fighting alongside Russian troops in the Ukraine war, South Korea’s Joint Chiefs of Staff said on Monday.

The new figure follows a report by Seoul’s spy agency to lawmakers last week, which said at least 100 North Korean soldiers had been killed since entering combat in December.

“Through various sources of information and intelligence, we assess that North Korean troops who have recently engaged in combat with Ukrainian forces have suffered around 1,100 casualties,” the South Korean military said in a statement.

“We are particularly interested in the possibility of additional deployments” of North Korean soldiers to aid Russia’s war effort, it added. Pyongyang is reportedly “preparing for the rotation or additional deployment of soldiers.”