Vladimir Putin has been accused of using deadly vacuum bombs in Russia's ongoing invasion of Ukraine.
The Ukrainian ambassador to the U.S. Oksana Markarova said the Kremlin had used the devastating bomb - which is banned by the Geneva convention - during air strikes.
More than 520,000 people are now said to have now fled Ukraine as refugees, with Vladimir Putin being accused of "war crimes", after residential areas in the city of Kharkiv were bombed by his regime
Read more: The faces and stories of the innocent children killed in the Russian invasion
Officially called Thermobaric weapons, the bombs are considered to be one of the most dangerous war weapons in the world and work by taking oxygen from the surrounding air to generate a high-temperature explosion.
They are filled with explosive fuel and chemicals and can set off supersonic waves on explosion with the ability to completely destroy everything in its path.
It comes after Putin ordered part of his nuclear forces to be on enhanced combat duty in an alarming escalation of tensions.
As the conflict enters its sixth day a US satellite image company says news images have shown a military convoy north of Kyiv now estimated to be 40 miles long.
Image of the convoy:
People in cities and towns across Ukraine were woken by air raid sirens this morning, urging people to find shelter as dawn broke.
There were also reports that a maternity hospital in village of Buzova, on the Zhytomyr highway where heavy fighting has been ongoing, had to be evacuated this morning after hit was hit by Russian shelling.
"No one in the world will forgive you for killing peaceful Ukrainian people," said Ukraine's President Volodymyr Zelensky, in an address late last night. Read the morning update here.
On Tuesday morning, the Ministry of Defence (MoD) said Russian forces have made "little progress" in their advance on Kyiv over the past 24 hours.
In an intelligence update posted to Twitter, MoD stated that this was likely due to "logistical difficulties".
The Department added: "Russian forces have increased their use of artillery north of Kyiv and in vicinities of Kharkiv and Chernihiv.
"The use of heavy artillery in densely populated urban areas greatly increases the risk of civilian casualties.
"Russia has failed to gain control of the airspace over Ukraine prompting a shift to night operations in an attempt to reduce their losses".
Meanwhile, Prime Minister Boris Johnson has left London for Warsaw where he is due to meet with Polish Prime Minister Mateusz Morawiecki.
Amid the Russian invasion of Ukraine, Boris Johnson is set to discuss the UK's financial and diplomatic support for central Europe as it faces the prospect of a humanitarian crisis.
Following the meeting he is set to fly to Estonia, where he will meet with leaders in Tallinn before visiting serving troops alongside Nato secretary-general Jens Stoltenberg.
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