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The Russian army will try to take full control over eastern and southern Ukraine, a top general was quoted as saying on Friday, a day after Moscow announced the "liberation" of Mariupol.
"Since the start of the second phase of the special operation ... one of the tasks of the Russian army is to establish full control over the Donbas and southern Ukraine," Maj Gen Rustam Minnekaev said, according to reports by Russian news agencies.
"This will provide a land corridor to Crimea," he said, referring to the peninsula Russia annexed from Ukraine in 2014.
Gen Minnekaev's comments were the most detailed description yet of Russia's goals in the second phase of its operation, which began after its troops pulled back from the Ukrainian capital Kyiv.
"Control over the south of Ukraine is another way out to Transnistria, where there are cases of Russian-speaking people being oppressed," Gen Minnekaev said.
Transnistria is a small breakaway region in the former Soviet republic of Moldova, where pro-Russia separatists are armed and backed by Moscow.
Moscow recognised the independence of the separatist Donetsk and Lugansk People's Republics in Ukraine's Donbas shortly before launching a military campaign on February 24 with the stated aim of protecting the Russian-speaking population there.
Western allies are preparing to offer Ukraine "security guarantees" which should make the country "impregnable" to a future Russian invasion, UK Prime Minister Boris Johnson said.
Mr Johnson said it is essential to step up immediate military support to Kyiv. He also said there is a "realistic possibility" that the conflict could drag on for a "long period".
He said Britain is looking to send tanks to "backfill" in Poland so that Soviet-era T-72s – with which Ukrainian crews are familiar – can be released to the government in Kyiv.
But speaking in the Indian capital, New Delhi, Mr Johnson said a long-term vision for Ukraine's place in the future "security architecture" of Europe also needs to be developed.
While he said it will not be the same as the Nato Article 5 guarantee – in which an attack on one member state is considered to be an attack on all – he hoped it would offer "deterrence by denial".
"What the Ukrainians want – and I think are now going to get – is a collection of guarantees from like-minded countries about what we can do to back them up with weaponry, with training and with intelligence-sharing," he said.
"It will, I hope, enable the Ukrainians to offer deterrence by denial and make sure their territory is so fortified as to be impregnable to further attack from Russia. That is what we need to do."
On Thursday, Russia announced what it described as the liberation of Mariupol in eastern Ukraine after besieging the strategic port city on the shores of the Sea of Azov for nearly two months.
Russia's change of strategic focus to southern and eastern Ukraine led to invading forces leaving behind a trail of indiscriminate destruction and civilian bodies around Kyiv, including in the commuter town of Bucha.
A United Nations mission to Bucha documented "the unlawful killing, including by summary execution, of some 50 civilians there", the UN's Office of the High Commissioner for Human Rights said.
"Russian armed forces have indiscriminately shelled and bombed populated areas, killing civilians and wrecking hospitals, schools and other civilian infrastructure, actions that may amount to war crimes," its spokesperson Ravina Shamdasani said.
The UN mission was sent on April 9, a week after an AFP team found bodies of people in civilian clothing lining the streets of Bucha, after the town had been under Russian occupation for more than a month.
There was no immediate response from Russia, but it has previously accused Ukrainian forces of staging the scene in Bucha, which when first reported triggered western criticism and redoubled sanctions against Moscow.
US satellite imagery company Maxar released photos that it said showed a "mass grave" on the north-west edge of Manhush, west of Mariupol.
UK police said they had received about 50 referrals relating to alleged war crimes in Ukraine, in support of an investigation by the International Criminal Court at The Hague.
Ukrainian officials say the bodies of more than 1,000 civilians have been retrieved from areas around Kyiv, and they are working with French investigators to document alleged war crimes.
"It's all being investigated," said Oleksandr Pavliuk, head of the Kyiv regional military administration. "There is no final number of civilians killed.
"The forensic experts are now examining the bodies. But what we saw was hands tied behind the back, their legs tied and shot through the limbs and in the back of the head," he said.
Ukrainian President Volodymyr Zelenskyy maintained a defiant tone in his latest video address.
With its claims about taking control of Mariupol, Russia was "doing everything to have a reason to talk about at least some victories", he said.
"They can only delay the inevitable – the time when the invaders will have to leave our territory, in particular Mariupol, a city that continues to resist Russia, despite everything the occupiers say."
Mr Zelenskyy accused Russia of laying the groundwork for a referendum to cement its control of separatist areas in the Donbas region of eastern Ukraine, urging locals to avoid giving personal data to Moscow's forces.
"This is aimed to falsify the so-called referendum on your land, if an order comes from Moscow to stage such a show," he said.
Separately, Mr Zelenskyy told leaders of the International Monetary Fund and World Bank that Ukraine now needs $7 billion a month to function, accusing Russia of "destroying all objects in Ukraine that can serve as an economic base for life".
Mr Zelenskyy meanwhile welcomed the latest promises of western military aid including, from the United States, howitzers, armoured vehicles, 144,000 rounds of ammunition and tactical drones.