France's foreign ministry spokesman on Thursday said he could not confirm Russia had launched an intercontinental ballistic missile in an attack on Ukraine but added such a move would be a serious escalation if reports are true.

Kyiv's air force earlier said Russia fired an intercontinental ballistic missile during an attack on the Ukrainian city of Dnipro, in what would be the first use in war of a weapon designed to deliver long-distance nuclear strikes.

"If confirmed we will react in an appropriate manner," Christophe Lemoine told journalists at a news conference.