Russian artillery pounded the Ukrainian cities of Mariupol and Kharkiv on Wednesday as the West prepared more sanctions against Moscow in response to civilian killings that Kyiv and its allies have called war crimes.

The besieged southern port of Mariupol has been under almost constant bombardment since the early days of the invasion that began on Feb. 24, trapping tens of thousands of residents without food, water or power.

"The humanitarian situation in the city is worsening," British military intelligence said on Wednesday.

"Most of the 160,000 remaining residents have no light, communication, medicine, heat or water. Russian forces have prevented humanitarian access, likely to pressure defenders to surrender."

Reuters could not immediately verify the report.

Ukraine's Deputy Prime Minister Iryna Vereshchuk said authorities would try to evacuate trapped civilians through 11 humanitarian corridors on Wednesday, though people trying to leave the besieged city of Mariupol would have to use their own vehicles. Read full story

Russian forces last week pulled back from positions outside the capital Kyiv and shifted their assault to the south and east, and Ukraine's general staff said the northeastern city of Kharkiv, the country's second-largest, also remained under attack.

Authorities in the eastern region of Luhansk on Wednesday urged residents to get out "while it is safe" from an area that Ukraine also expects to be the target of a new offensive. Read full story

Sanctions push

Western sanctions over Russia's invasion of Ukraine, described as a "special military operation" by Moscow and the biggest assault on a European nation since World War Two, gained new impetus this week after dead civilians shot at close range were found in the northern town of Bucha after it was retaken from Russian forces.

Moscow denied targeting civilians there and called the evidence presented a forgery staged by the West to discredit it.

New sanctions set to be unveiled Wednesday are in part a response to Bucha, the White House said.

Coordinated between Washington, the Group of Seven advanced economies and the European Union, the measures will target Russian banks and officials and ban new investment in Russia, the White House said.

Proposed EU sanctions would ban buying Russian coal, prevent Russian ships from entering EU ports, and suspend nearly 20 billion euros ($21.77 billion) worth of trade.

EU executive chief Ursula von der Leyen said the bloc was working on banning oil imports as well as part of a plan to end its dependence on Russian energy.

Europe obtains about a third of its natural gas from Russia and Ukraine says banning Russian gas is vital to securing a deal to end the war in peace talks.

After an impassioned address to the UN Security Council on Tuesday, Zelenskiy said new sanctions against Russia "must be commensurate with the gravity of the occupiers' war crimes," calling it a "crucial moment" for Western leaders.

New Zealand said on Wednesday it would impose a 35% tariff on all imports from Russia and extend export bans on industrial products connected to strategic Russian industries.

"The images and reports emerging of atrocities committed against civilians in Bucha and other regions of Ukraine is abhorrent and reprehensible," Foreign Minister Nanaia Mahuta said in a statement.

The United States has agreed to provide an additional $100 million in assistance to Ukraine, including Javelin anti-armour systems, the Pentagon said on Tuesday.

US chipmaker Intel Corp INTC.O said it had suspended business operations in Russia, joining a growing list of companies leaving the country.

Bucha burial

Ukrainian officials say between 150 and 300 bodies might be in a mass grave by a church in Bucha, north of the capital Kyiv.

Satellite images taken weeks ago show bodies of civilians on a street in the town, a private U.S. company said.

Reuters reporters saw at least four victims shot through the head in Bucha, one with their hands tied behind their back.

Residents have recounted cases of several others slain, some shot through their eyes and one apparently beaten to death and mutilated.

Since launching an invasion that has uprooted a quarter of Ukraine's population, Russia has failed to capture a single major city.