BUCHA -- Police and other investigators walked the silent streets of ruined towns around Ukraine's capital, documenting widespread killings of unarmed civilians and other alleged war crimes by Russian forces that could draw tougher Western sanctions as soon as Wednesday.

Ukrainian President Volodymyr Zelenskyy has kept up demands for war-crimes trials for Russian troops and their leaders, while warning they were regrouping for fresh assaults on Ukraine's east and south.

Overnight, Russian forces attacked a fuel depot and a factory in Ukraine's Dnipropetrovsk region, the region's governor Valentyn Reznichenko said on the messaging app Telegram early Wednesday. The number of casualties was unclear.

"The night was alarming and difficult. The enemy attacked our area from the air and hit the oil depot and one of the plants. The oil depot with fuel was destroyed. Rescuers are still putting out the flames at the plant," Reznichenko wrote.

In the eastern Luhansk region, shelling of the Rubizhne city on Tuesday killed one person and injured five more, its governor Serhiy Haidai said on Telegram.

Police in the Romanian capital Bucharest said a car rammed the gate of the Russian Embassy early Wednesday, bursting into flames and killing the driver. There was no immediate information on a possible motive or other details.

Ukraine's military has said Russian troops were focused on preparing for an offensive in Ukraine's east, with the aim "to establish complete control over the territory of Donetsk and Luhansk regions." Parts of the two regions have been under control of Russia-backed rebels since 2014 and are recognized by Moscow as independent states.

So far, Ukrainian forces have been holding back Russian troops trying to push east but remain outnumbered in both troops and equipment, Zelenskyy said in a video address to his country late Tuesday.

"But we don't have a choice _ the fate of our land and of our people is being decided," he said. "We know what we are fighting for. And we will do everything to win."

Over the past few days, a global outcry has been raised over what appear to be intentional killings of civilians in Bucha and other towns before Russian forces withdrew from the outskirts of Kyiv. The evidence led Western nations to expel scores of Moscow's diplomats and propose further sanctions.

The US, in coordination with the European Union and Group of Seven big economies, is expected to roll out more sanctions Wednesday, including a ban on all new investment in Russia, a senior administration official said, speaking on condition of anonymity to discuss the upcoming announcement.

Also, the EU's executive branch proposed a ban on coal imports from Russia, which are an estimated 4 billion euros ($4.4 billion) per year. It would be the first time the 27-nation bloc has sanctioned the country's lucrative energy industry over the war.

Speaking by video Tuesday to the UN Security Council, Zelenskyy said civilians in towns around Kyiv were tortured, shot in the back of the head, thrown down wells, blown up with grenades in their apartments and crushed to death by tanks while in cars.

Those who carried out the killings and those who gave the orders "must be brought to justice immediately for war crimes" in front of a tribunal similar to the one established at Nuremberg after World War II, he said.

Moscow's UN ambassador, Vassily Nebenzia, said "not a single local person" suffered from violence while Bucha was under Russian control, and, reiterating Kremlin comments, said video footage of bodies in the streets was "a crude forgery" staged by the Ukrainians.

"You only saw what they showed you," he said. "The only ones who would fall for this are Western dilettantes."

As Zelenskyy spoke to the diplomats, survivors of the monthlong Russian occupation showed investigators bodies of townspeople allegedly shot by Russian troops.

In the still largely empty streets of Bucha, dogs wandered among ruined buildings and burned military vehicles. Officials snapped photos of the corpses before gathering some of them.

Survivors who hid in their homes during the occupation, many of them beyond middle age, wandered past charred tanks and jagged window panes with plastic bags of food and other humanitarian aid. Red Cross workers checked in on intact homes.

Associated Press journalists in Bucha have counted dozens of corpses in civilian clothes and interviewed Ukrainians who told of witnessing atrocities. Also, high-resolution satellite imagery from Maxar Technologies showed that many of the bodies had been lying in the open for weeks, during the time that Russian forces were in the town.

The dead in Bucha included a pile of six charred bodies, as witnessed by AP journalists. It was not clear who they were or under what circumstances they died. One body was probably that of a child, said Andrii Nebytov, head of police in the Kyiv region.

Many of the dead seen by AP journalists appeared to have been shot at close range, and some had their hands bound or their flesh burned.

The AP and the PBS series "Frontline" have jointly verified at least 90 incidents during the war that appear to violate international law. The War Crimes Watch Ukraine project is looking into apparent targeted attacks as well as indiscriminate ones.

US Secretary of State Antony Blinken said the images from Bucha revealed "not the random act of a rogue unit" but "a deliberate campaign to kill, to torture, to rape, to commit atrocities." He said the reports of atrocities were "more than credible."

The chief prosecutor for the International Criminal Court at The Hague opened an investigation a month ago into possible war crimes in Ukraine.

Elsewhere in Ukraine, in Borodyanka, northwest of Kyiv, a 25-year-old, Dmitriy Yevtushkov, searched the rubble of apartment buildings and found that only a photo album remained from his family's home.

In the besieged southern city of Mykolaiv, a passerby stopped briefly to look at the bright blossoms of a shattered flower stand lying among bloodstains, the legacy of a Russian shell that killed nine people in the city's center. The onlooker sketched the sign of the cross in the air, and moved on.

NATO Secretary-General Jens Stoltenberg, meanwhile, warned that in pulling back from the capital, Russia's military is regrouping its forces in order to deploy them to eastern and southern Ukraine for a "crucial phase" of the war. "Moscow is not giving up its ambitions in Ukraine," Stoltenberg said.

While both Ukrainian and Russian representatives sent optimistic signals following their latest round of talks a week ago, Russian Foreign Minister Sergey Lavrov said Moscow will not accept a Ukrainian demand that a prospective peace deal include an immediate pullout of troops followed by a Ukrainian referendum on the agreement. (AP)