Though North Korean ballistic missiles account for only a small portion of Russia's missile strikes they carry a large warhead of up to one tonne and have a range of up to 800 km, the military source said. The Iskander-M, an equivalent Russian missile, carries a smaller payload and has a shorter range of 500 km.

Russian missile attacks on state-owned natural gas assets in Ukraine have forced the country to buy expensive replacement fuel from the European Union, according to people with knowledge of the matter.

A Russian strike killed five civilians and wounded 55 on Tuesday in the town of Izium in Ukraine's northeastern Kharkiv region, partially destroying the city council building, officials said.