Russia may use its new Oreshnik hypersonic missile to attack "decision-making centres" in Kyiv in response to Ukraine's firing of Western missiles at Russian territory, President Vladimir Putin said on Thursday.

Russia’s widespread overnight attack targeting critical energy infrastructure facilities in Ukraine was a response to strikes on Russian territory using US-made ATACMS missiles, President Vladimir Putin said Thursday.

A nationwide air raid alert was sounded in Ukraine early on Thursday, with reports of explosions in several cities. The Ukrainian air force said in a Telegram post at 05:19 local time (03:19 GMT) that the alert was in force "throughout the territory of Ukraine due to the threat of missile danger".

Vladimir Putin was greeted with a display of a Ukrainian flag while visiting Kazakhstan for a summit where he is expected to discuss the war in Ukraine.

Ukraine's flag - with its horizontal bands of blue and yellow - briefly appeared late on Wednesday instead of the Russian white, blue and red tricolor on a screen located on one of Astana's main thoroughfares.