North Korea has started sending troops to fight with Russia in Ukraine, South Korea's spy agency has said as Seoul warned of a "grave security threat". The allegation comes a day after Ukrainian President Volodymyr Zelensky said he believed 10,000 North Korean soldiers could join the war, based on intelligence information.

"The National Intelligence Service said it has learned that the North has recently decided to send four brigades of 12,000 soldiers, including special forces, to the war in Ukraine," Yonhap said. The NIS declined to confirm the report to AFP. "The movement of North Korean troops has already begun," an NIS source told Yonhap.

Volodymyr Zelenskyy has said a formal invitation to join Nato is “the only way” Ukraine can survive Russia’s invasion, as the Ukrainian president urged western allies to endorse his plan to end the war.