South Korea has summoned the Russian ambassador, seeking the “immediate withdrawal” of North Korean troops which it says are being trained to fight in Ukraine.

About 1,500 North Korean soldiers, including those from the special forces, have already arrived in Russia, according to Seoul’s spy agency.

In a meeting with the ambassador Georgiy Zinoviev, South Korea’s vice-foreign minister Kim Hong-kyun denounced the move and warned that Seoul will “respond with all measures available”.