Ukraine war: Video shows building engulfed in fireball after Russian missile strike

Watch: Video shows building being blown to bits by devastating Russian missile strike

This is the moment a local government building in Kharkiv was engulfed in a huge fireball by a devastating Russian missile strike.

Footage was posted to social media by Kharkiv region head Oleg Synegubov, showing the Region State Administration Building disappearing into a ball of flames.

Six people were injured in the attack, including a child, the state emergencies agency said.

Ukraine's Foreign Minister, Dmytro Kuleba, demanded more international sanctions against Russia after what he said was a "barbaric" attack on the country's second largest city.

"Barbaric Russian missile strikes on the central Freedom Square and residential districts of Kharkiv. Putin is unable to break Ukraine down. He commits more war crimes out of fury, murders innocent civilians," Kuleba said on social media.

"The world can and must do more. INCREASE PRESSURE, ISOLATE RUSSIA FULLY."

Read more: Russian advance on Kyiv 'makes little progress over 24 hours'

The explosion comes amid fears Vladimir Putin could resort to more barbaric tactics after failing to make any significant gains in Ukraine.

He had reportedly expected to invade within days, but he is now six days in and facing huge resistance from the Ukrainian people.

One of his key aims will be to take the capital city of Kyiv under Russian control, but civilians and the armed forces have so far held off their advances.

On Monday, Russia was accused of war crimes after a reported cluster bomb attack on Kharkiv, which reportedly killed 11 people.

Ukrainian President Volodymyr Velenskyy said in a late-night address there would "definitely be an international tribunal" for what he said was a "violation of all conventions".

He added: "No one in the world will forgive you for killing peaceful Ukrainian people."

Satellite images released on Tuesday morning have revealed a huge 40-mile long convoy of Russian vehicles heading towards Kyiv, amid fears Putin is ready to ramp up his efforts to take the capital.

Boris Johnson warned Putin was using “barbaric and indiscriminate tactics against innocent civilians” during a trip to Poland to discuss the ongoing situation.

He said the Russian President was prepared to “bomb tower blocks, to send missiles into tower blocks, to kill children, as we are seeing in increasing numbers”.

Speaking in Warsaw, Johnson said in the “grim war” Putin had “fatally underestimated” the resistance of the Ukrainians and the resolve of the West to act.

The prime minister paid tribute to the “leadership and courage” of Volodymyr Zelensky, the Ukrainian president.

“I think he has inspired and mobilised not only his own people, he is inspiring and mobilising the world in outrage at what is happening in Ukraine,” Johnson added.

Synegubov said Russian missile attacks had hit the centre of Kharkiv, including residential areas and the regional administration building.

He claimed Russia had launched GRAD and cruise missiles on Kharkiv but that the city defence was holding.

"Such attacks are genocide of the Ukrainian people, a war crime against the civilian population!" he said.

Wearing a flak jacket and a helmet, Synegubov said in a video posted on social media on Tuesday morning that it was too early to know the number of casualties.

Russia calls its actions in Ukraine a “special operation” that it says is not designed to occupy territory but to destroy its southern neighbour's military capabilities and capture what it regards as dangerous nationalists.

However, the slower-than-expected pace of the Russian invasion has given rise to fears that frustrated Russian commanders could resort to even more devastating tactics.