The US and the EU moved Friday to tighten the economic noose around the Kremlin as Russian forces inched toward the capital Kyiv and pounded civilian areas of Ukrainian cities, drawing a flurry of warnings of potential war crimes.

US Vice-President Kamala Harris said Russian President Vladimir Putin "shows no sign of engaging in serious diplomacy" to end the war he launched on February 24.

Harris spoke in Bucharest, her latest stop on a tour of Ukraine's EU and NATO neighbours, former Soviet satellites, to reassure them the transatlantic alliance is solid as Putin ratchets up his denunciation of NATO's eastward advance since communism collapsed in the 1990s.

Keen to avoid a direct military intervention in non-NATO Ukraine that they fear could trigger World War III, the allies announced further steps to increase the economic pressure on the Kremlin to rein in its forces.

President Joe Biden said Friday the US and its allies would end normal trade relations with Russia and announced a ban on imports of Russian vodka, diamonds and seafood. The US will also ban the export of US luxury goods to Russia and Belarus.

"Putin must pay the price. He cannot pursue a war that threatens the very foundation of international peace and stability and then ask for help from the international community," Biden said.

EU chief Ursula von der Leyen said that Brussels will ban the export of luxury goods to Russia, striking a "direct blow to the Russian elite."

US and European stock markets had risen earlier, buoyed by Putin's comments about "certain positive shifts" in negotiations with Ukraine.

 'Can't help anyone'

The first high-level talks between the two sides on Thursday failed to make a breakthrough, but Putin said negotiations are "now being held on an almost daily basis".

But Harris said Putin was not serious about diplomacy.

"That's why we engaged in historic sanctions, with the effect of a free falling ruble, the Russian stock market is still not open, their credit ranking is now junk," the vice president said, warning of further sanctions against Russia's "atrocious and outrageous conduct."

The situation is particularly dire in the southern port city of Mariupol where local officials said Friday more than 1,500 people have been killed during 12 days of Russian siege.

There was also no let up in the bombardment, with three missiles hitting civilian buildings in the central city of Dnipro early Friday, destroying a shoe factory and killing a security guard.

The industrial hub of one million inhabitants had been considered a relatively safe haven, a centre for coordination of humanitarian aid and those fleeing more severe fighting in the country's east.

But images of its charred or destroyed buildings -- including a kindergarten with windows blown out -- now join those from Kharkiv and Mariupol as testimony to the brutal conflict.

 Syrian 'mercenaries'

Russia also announced the military airfields of Lutsk and Ivano-Frankivsk, in western Ukraine closer to the Polish border, had been "put out of action".

Local officials said four Ukrainian servicemen were killed in the attack.

Ukraine claimed the widening of Russia's targets followed its failure to secure cities already under siege, and insisted Moscow had made no "significant progress" in the last 24 hours.

But the capital Kyiv risks being entirely surrounded, with presidential adviser Mykhailo Podolyak calling it a "city under siege".

He tweeted that it was "ready to fight", with checkpoints prepared and supply lines in place, adding: "Kyiv will stand until the end".

The Ukrainian military warned on Thursday Russia was trying to "block" Kyiv by taking out defences to the west and north of the capital, adding that there was also a risk to Brovary in the east.

The northwest suburbs, including Irpin and Bucha, have already endured days of heavy bombardment but Russian armoured vehicles are also advancing on the northeastern edge.

Ukrainian soldiers described fierce fighting for control of the main highway leading into the capital, and AFP reporters saw missile strikes in Velyka Dymerka just outside Kyiv's limits on Thursday.

Turkey, one of the last countries to keep its embassy open in Kyiv, said Friday it had was beginning to evacuate staff.

Britain's defence ministry said Russian forces were committing more forces to encircle key cities, reducing numbers available to continue the advance.

The Kremlin on Friday announced that Syrian fighters can fight for Russia in Ukraine after Putin backed plans to draft in 16,000 volunteers, mostly from the Middle East.

Ukrainian President Volodymyr Zelensky accused Russia of hiring "murderers from Syria, a country where everything has been destroyed... like they are doing here to us".

 Military aid boost

In a video message recorded outside his presidential office in Kyiv, Zelensky also demanded the European Union "do more" to help his country.

Around 100,000 people have been able to leave the northeastern city of Sumy, the eastern city of Izyum, and areas northwest of Kyiv in the last two days, Ukrainian officials said.

But the president warned living conditions were deteriorating fast, in the northeast, around the capital and in the east.

EU leaders on Friday sought to double financing for military aid to Ukraine by an extra 500 million euros (around $550 million).

Late Thursday the US congress passed a budget including $14 billion in humanitarian and military aid to the country.

But the US has ruled out enforcing a no-fly zone, and rejected a Polish plan to transfer fighter jets to Ukraine via a US air base for fear of being drawn directly into the conflict.

 Severe price

In Mariupol, Mayor Vadym Boichenko said Russian warplanes had targeted residential areas in the city "every 30 minutes" on Thursday, "killing civilians, the elderly, women and children".

Harris, the International Criminal Court in The Hague and the UN human rights office in Geneva all warned Friday that attacks on civilians were banned and could amount to war crimes.

Zelensky accused Moscow of launching a "tank attack" targeting a humanitarian corridor to which he had dispatched a convoy to try to get food, water and medicine into the city.

On Wednesday, he and top Western officials also accused Russia of a "war crime" for the bombing of a children's hospital there that local officials said killed three people, including a young girl.

Russia's army claimed the bombing was a "staged provocation" by Ukraine.

The International Committee of the Red Cross said some Mariupol residents had started fighting for food, and many had run out of drinking water.

Later Friday, the UN Security Council will hold an emergency meeting at Russia's request, over its claims that the US is funding research into the development of biological weapons in Ukraine.

Both Washington and Kyiv have denied the allegations.