LVIV, UKRAINE (REUTERS) - Russia gave the most sombre assessment so far of its invasion of Ukraine, describing the "tragedy" of mounting troop losses and the economic hit from sanctions, as Ukrainians were evacuated from eastern cities before an anticipated major offensive.

Moscow’s six-week long incursion has seen more than 4 million people flee abroad, killed or injured thousands, turned cities into rubble and led to sweeping sanctions on Russian leaders and companies.

In a symbolic move, the United Nations General Assembly suspended Russia from the UN Human Rights Council, expressing "grave concern at the ongoing human rights and humanitarian crisis". Russia then quit the council.

Moscow has previously acknowledged that its attack has not progressed as quickly as it wanted, but on Thursday (April 7), Kremlin spokesman Dmitry Peskov lamented the rising death toll.

“We have significant losses of troops,” he told Sky News.“It’s a huge tragedy for us.”

Russia is facing its most difficult economic situation for three decades due to unprecedented Western sanctions, Prime Minister Mikhail Mishustin said.

The United States Congress removed its “most favoured nation” trade status and Washington blacklisted two Russian state-owned companies, a shipbuilding firm and a diamond miner as it sought to starve Russia’s “war machine”.

Russia says it launched what it calls a “special military operation” on Feb 24 to demilitarise and “denazify” Ukraine.

Kyiv and its Western allies reject that as a false pretext.

Following new restrictions after the killing of civilians in Bucha, a town on the west of the capital Kyiv, that were widely condemned by the West as war crimes, Ukraine called on allies to stop buying Russian oil and gas, amid divisions in Europe, and to boost it militarily.

“Ukraine needs weapons which will give it the means to win on the battlefield and that will be the strongest possible sanction against Russia,” President Volodymyr Zelensky said in a video late on Thursday.

He also said the situation in Borodyanka – another town north-west of Kyiv retaken from Russian forces – is "significantly more dreadful" than in Bucha, without citing any evidence.

Video from Borodyanka showed search and rescue teams using heavy equipment to dig through the rubble of a building that collapsed. Hundreds of people were feared buried.

Moscow has denied targeting civilians and says images of bodies in Bucha were staged to justify more sanctions against Moscow and derail peace negotiations.

The European Union’s ambassadors agreed a fifth sanctions package on Russia with a coal embargo containing a 120 day wind-down period to give member states time to find alternative suppliers, following pressure from Germany to delay the measure.

Ukraine accused Hungary of undermining EU unity after Budapest said it was prepared to pay roubles for Russian gas, a Kremlin demand that most in the West had resisted.

On the battlefield, Ukraine says after withdrawing from Kyiv’s outskirts, Russia is regrouping to try to gain full control over the eastern regions of Donetsk and Luhansk, which have been partly held by Russian-backed separatists since 2014.

The besieged southern port of Mariupol, where the mayor said over 100,000 people were still trapped, was also a target.

“Evacuate! The chances of saving yourself and your family from Russian death are dwindling every day,” Luhansk governor Serhiy Gaidai said.

Authorities in Dnipro, a city in central-eastern Ukraine, also urged women, children and the elderly to leave.

Trading accusations

Both sides continued to trade accusations, with Moscow opening a criminal investigation into a Russian soldier’s allegations that he was beaten and threatened with death while being held in Ukraine as a prisoner of war.

Separately, a social media video verified by Reuters and geolocated to an area west of Kyiv appears to show Ukrainian forces shooting and killing a captured and badly wounded Russian soldier.

Nato members agreed to strengthen support to Ukraine on Thursday.

Ukraine has received about 25,000 anti-aircraft weapons systems from the US and its allies, the top US general said, and Washington is looking into what new support it could send.

In a video address posted on YouTube, Ukrainian Defence Minister Oleksii Reznikov made a plea for heavier, more modern weapons as Russia concentrated its forces for a powerful attack.

Russia has “drawn conclusions and changed tactics” and is now focusing on long-range strikes from the air.

As a result, Ukraine needs air defence systems, long-range artillery, tanks and anti-ship missiles, Reznikov said.

Zelenskiy’s government says starving Moscow’s war machine is the only way to bring it to a settlement at on-and-off peace talks.

On Thursday, Russian Foreign Minister Sergei Lavrov said a draft peace deal from Kyiv contained “unacceptable” elements and deviated from previously agreed proposals.

Ukrainian negotiator Mykhailo Podolyak told Reuters that Mr Lavrov was not directly involved in negotiations and his statements were “of purely propagandistic significance” aimed at diverting attention from killings in Bucha.

Since Russian troops pulled back last week, Ukrainian officials have said that hundreds of civilians have been found dead.

Bucha’s mayor has said dozens were the victims of extra-judicial killings carried out by Russian troops. Reuters could not independently verify those figures.

In an unusual public comment on the conflict by a large Russian company, the chairman of aluminium giant Rusal called for an impartial investigation into the killing of civilians in Bucha.

Accounts by at least a dozen residents of one apartment complex in Bucha painted a picture of violence and intimidation by Russian soldiers.

The mutilated bodies of one resident of the complex and another local were discovered in a stairwell.