There is a desperate hunt for the Butchers of Bucha after women and children were raped and shot by Russians, according to Ukrainian sources.
Deeply disturbing reports began emerging from the town over the weekend which the invading forces left in front of a trail of destruction.
It is feared that local women and children have been raped and civilians shot mercilessly and left in the street to die.
The numbers of dead in the Kyiv Oblast town are suspected to stretch into the hundreds.
Lt Colonel Azatbek Omurbekov, which leads the 64th Separate Motorised Rifle Brigade which occupied Bucha, is the first senior military official connected to the massacre to be named.
Ukrainian reporter Evgeny Spirin said: “Some of the killed children had their arms tied up. Children…. They were tying up children. There were shot dogs."
He added: “Irpen, Bucha, Dmitrievka. How to live with this, and is it worth living at all?
“How do I explain this to myself, how? They must cease to exist.
“They must all be destroyed, each and every one of them, turned into dust, into mud, into clay, all of them.”
Ukrainian activists and web sleuths have identified the presence of Omurbekov’s forces - which are normally based in the far east of Russia rather than Kyiv Oblast - and a number of other Russian military units.
Volunteers group Tretya Sila reported: "In Bucha there was a military unit 51460 from the village of Knyaze-Volkonskoye, Khabarovsk region...
“Soon all these murderers, rapists and looters will be known by name."
InformNapalm volunteers named Omurbekov as unit 51460 of the 64th Separate Motorized Rifle Brigade amid suspicions of grotesque war crimes in Bucha.
Forces from several other groups are also suspected of being in the town, including those from the Fifth Separate Guards Tank Brigade of 36th army of the Russian Eastern military district and the 331st Parachute Assault Regiment of 98th airborne division.
So far Omurbekov is the only commander to be named.
Russian sources have denied that they are responsible for the massacre, claiming that the Ukrainian army slaughtered its own people.
Russian ambassador to the US Anatoly Antonov said: “The Russian defence ministry has fully rejected these false accusations.
”I would like to point out that Russian troops left Bucha on March 30.
“The Ukrainian authorities remained silent all these days, and now they have suddenly posted sensational footage in order to tarnish Russia’s image and make Russia defend itself.
"I would like to emphasise with full responsibility that not a single civilian suffered from violence when the town was controlled by the Russian Armed Forces.
"On the contrary, our troops delivered 452 tonnes of humanitarian aid for civilians.
"Meanwhile, the fact that the Ukrainian Armed Forces shelled the town of Bucha right after Russian troops had left was deliberately ignored in the US.
“This is what could have caused civilian casualties. That said, the Kiev regime is clearly trying to blame its atrocities on Russia.”
Foreign ministry spokeswoman Maria Zakharova claimed Kyiv colluded with the West in seeking to blame Russia for the massacre, which she said was "a provocation staged by the Ukrainian military and radical nationalists” to disrupt peace talks.
The unsupported claims from Russian officials are typical of those which have been heard throughout the invasion and clearly aim to sow doubt and division within Ukraine and its allies.
The scale of the massacre and its depraved nature has prompted a response from Western leaders, while it has been reported that Boris Johnson will seek to galvanise a tough response from allies to the crisis.
On its 73rd anniversary, the Prime Minister will hail Nato as the "greatest security alliance in the history of the world" - adding that it has a responsibility to support the Ukrainian people as they fight for freedom with "every fibre of their being".
It comes after the PM condemned Russia's "despicable attacks" against Ukrainian civilians in Irpin and Bucha, adding that "we will not rest until justice is served".
This week he will welcome the Polish and German leaders to Downing Street for discussions on Nato and how to support Ukraine as it stands up to Russian aggression.
On Sunday, Mr Johnson said "no denial or disinformation from the Kremlin" can conceal that President Vladimir Putin is "desperate" and "his invasion is failing".
An adviser to Ukrainian president Volodymyr Zelensky said dead civilians had been found on the streets of the small city of Bucha and the Kyiv suburb of Irpin, in what resembled a "horror movie".
In Bucha, north-west of Kyiv, Ukrainian soldiers used cables to drag bodies off a street - from a distance due to fears they may be booby-trapped - as Russian troops withdraw and focus attacks on other parts of Ukraine.
Ukraine's prosecutor-general Iryna Venediktova said the bodies of 410 civilians have been found in Kyiv-area towns that were recently retaken from Russian forces.
In a statement, Mr Johnson said the UK was "stepping up" its sanctions and military support, and "bolstering" humanitarian help for those on the ground.
He added: "The UK has been at the forefront of supporting the International Criminal Court's (ICC) investigation into atrocities committed in Ukraine.
"The Justice Secretary has authorised additional financial support and the deployment of specialist investigators - we will not rest until justice is served."
Earlier on Sunday, Foreign Secretary Liz Truss said "indiscriminate" attacks by Russian forces against innocent civilians in Irpin and Bucha must be investigated as war crimes.
Ms Truss said the UK would "not rest" until those responsible for "atrocities" in Ukraine had faced justice, adding that Russia would not be allowed to cover up its involvement through "cynical disinformation".
Mr Zelensky's spokesman Sergey Nikiforov said authorities in Ukraine had found what looked "exactly like war crimes", including the bodies of executed civilians and mass graves.
