Russian Defense Ministry spokesman Igor Konashenkov. (Photo: RIA Novosti)

Defence ministry spokesman Igor Konashenkov said in a video briefing that they know for sure that Ukrainian combat aircraft had flown to Romania and other neighbouring countries.

He added that the use of the airfield network in these countries for basing Ukrainian military aviation with the subsequent use of force against Russia's army can be regarded as the involvement of these states in an armed conflict.

Russia have declared a temporary cease-fire to open humanitarian corridors for four Ukrainian cities including the capital Kyiv, Kharkov, Sumy and Mariupol. The decision was taken based on the humanitarian situation in these cities and at the personal request of French President Emmanuel Macron to Russian President Vladimir Putin.

The humanitarian corridors opened at 10:00 Moscow time, 14:00 on Monday Vietnam time.