Russian oil giant Lukoil on Thursday called for an immediate halt to fighting in Ukraine, one of the first major domestic firms to speak out against Moscow's military operation of its pro-Western neighbour.

The company said in a statement its board backs "the immediate cessation of the armed conflict and fully supports its resolution through the negotiation process and through diplomatic means".

This comes even as Ukraine's emergency service says at least 22 people have been killed in Russian air raids on Ukraine's northern Chernihiv region.

The service said in a post on Twitter that rescue work was ongoing. It did not specify where the alleged attack took place.

Earlier the regional governor said at least nine people had been killed by an air raid on two schools and private houses.

(With input from agencies)