A Russian AN-26 military transport aircraft crashed in Russia's southern Voronezh region on Thursday, killing its crew on board, Interfax news agency quoted Russian military officials as saying.

The accident could have been caused by a technical failure and has not inflicted any damage on the ground, Interfax said, citing a press office of Russia's western military district.

Days after Russia's Security Council "recognised the independence" of Donetsk and Luhansk in eastern Ukraine, President Vladimir Putin on Thursday ordered a military invasion of Ukraine.

In a televised address, Putin said he had ordered a "special military operation" in Ukraine to "protect Russians" in the separatist regions. The claim was in line with fears voiced by the US and its European allies that Russia could invade Ukraine on the false pretext of "Ukrainian aggression".

Russia's decision to send troops into Ukraine triggered sharp responses from world leaders, with many of them calling for tougher sanctions against Putin and his closest aides.

US President Joe Biden condemned Russia for its "unprovoked and unjustified attack" on Ukraine. Biden, while promising that the US and its allies will hold Russia accountable, said the G7 have agreed on "devastating packages of sanctions" against Russia.

French President Emmanuel Macron said the Russian invasion of Ukraine is a "turning point" for Europe. His British counterpart Boris Johnson called President Vladimir Putin a "dictator", while German Chancellor Olaf Scholz accused Russia of trying to "wipe Ukraine off the map".

China, however, backed Russian military action in Ukraine, saying that it "understands Moscow's reasonable concerns on security issues" over Ukraine.

(With inputs from agencies)