Russian airstrikes hit a residential block in Kharkiv and the main TV tower in the capital Kyiv, Ukraine said on Tuesday, as Moscow stepped up attacks despite sanctions and warnings of a humanitarian crisis.

Eight people were reported killed in the strike in Kharkiv, Ukraine's second-biggest city, on day six of Russia's invasion of its pro-Western neighbour.

Kharkiv officials said 10 more people had been killed by Russian shelling on a local government building, and 10 more were found alive under the rubble.

Ukrainian officials said the strike on the TV tower in Kyiv killed five people, knocked out some state broadcasting but left the structure intact.

It came after Russia warned Kyiv residents living near security infrastructure to leave their homes.

"This is state terrorism on the part of Russia," said Ukrainian President Volodymyr Zelensky, accusing Moscow of committing a "war crime".

After a call with US President Joe Biden later Tuesday he said on Twitter: "We must stop the aggressor as soon as possible." 

Russia has denied targeting civilian infrastructure.

Visiting Estonia on Tuesday, British Prime Minister Boris Johnson called the bombardment of Kharkiv "absolutely sickening" and reminiscent of massacres of civilians in Sarajevo in the 1990s.

Strategic win along Azov Sea 

The International Criminal Court has already opened a war crimes investigation against Russia since Moscow began its invasion on Thursday.

Ukraine says more than 350 civilians, including 14 children, have been killed in the conflict so far.

There was no breakthrough in initial talks between Russia and Ukraine Monday and Russian forces have pressed further into the country.

In southern Ukraine, the city of Mariupol on the Azov Sea was left without electricity after bombardment, while Kherson on the Black Sea reported Russian checkpoints encircling the city.

In a key victory for Moscow, Russia's defence ministry said its troops had linked up with the forces of pro-Moscow rebels from eastern Ukraine in a region along the Azov Sea coast.

But Ukrainian forces say that despite incursions by "sabotage groups" into the cities, Russian forces have yet to capture a major settlement.

Shattered peace in Europe

During a visit to an airbase in Poland, NATO chief Jens Stoltenberg said Russian President Vladimir Putin had "shattered peace in Europe".

Zelensky meanwhile reiterated an urgent appeal for his pro-Western country to be admitted to the European Union.

"Prove you are not abandoning us and you are really Europeans," he told MEPs in a video address to the European Parliament. 

More than 660,000 people have already fled abroad, the UN refugee agency said, estimating that a million people are displaced within ex-Soviet Ukraine, which has a population of 44 million.

The UN estimates that up to four million refugees may need help in the coming months and 12 million more will need assistance within the country.

It has asked for $1.7 billion in urgent aid, while the EU pledged 500 million euros.

Russia has defied international bans, boycotts and sanctions to press ahead with an offensive it says is aimed at defending Ukraine's Russian speakers and toppling the leadership.

Defence Minister Sergei Shoigu said Russia would continue "until set goals are achieved".

He vowed to "demilitarise and de-Nazify" Ukraine and protect Russia from a "military threat created by Western countries".

Western powers are planning more sanctions in response, with French Finance Minister Bruno Le Maire saying they would "bring about the collapse of the Russian economy".

Russia's former president Dmitry Medvedev, the deputy head of Russia's Security Council, hit back, warning that "economic wars quite often turned into real ones" in the past.

Bombing kept us up all night

Fears are growing of an all-out assault to capture Kyiv -- a city of 2.8 million people.

Satellite images provided by US firm Mazar showed a 65-kilometre (40-mile) long build-up of armoured vehicles and artillery north of the city.

Zelensky said defending the city was now "the key priority for the state".

Inside Kyiv, makeshift barricades dotted the streets and residents formed long queues outside the few shops that remained open to buy basic essentials.

In the village of Shaika near Kyiv, Natasha, 51, opened a canteen in the local church to feed soldiers and volunteers.

"The shelling and the bombing kept us up all night," she said.

Sanctions hit Russians 

Western nations have moved to further isolate Russia, responding with an intensifying diplomatic, economic, cultural and sporting backlash.

US Secretary of State Antony Blinken on Tuesday suggested Russia should be stripped of UN rights council membership.

Germany has already promised arms for Ukraine, while the EU also said it will buy and supply arms to Ukraine, the first such move in its history.

Turkey said it would implement an international treaty to limit ships passing through the Dardanelles and Bosphorus straits, a move requested by Ukraine to block the transit of Russian warships.

And global shipping magnates Maersk, MSC and CMA CGM all said Tuesday they were suspending non-essential deliveries to Russia in the latest economic punishment. 

Within Russia, sanctions imposed by the West have begun to bite.

Putin announced emergency measures intended to prop up the Russian ruble, including banning Russians from transferring money abroad, after the currency crashed to a record low.

Many ordinary Russians have raced to withdraw cash.

Russian conductor sacked 

The response from the world of sports also gathered steam.

Russia was expelled from the World Cup and the country's clubs and national teams suspended from all international football competitions, while the International Tennis Federation banned Russian and Belarusian teams from competitions. 

The International Olympic Committee on Monday urged sports federations and organisers to exclude Russian and Belarusian athletes and officials from international events.

Russian ally Belarus hosted some troops used in Moscow's invasion.  

In the arts, the Munich Philharmonic said it was parting ways with star Russian conductor Valery Gergiev "with immediate effect" after he failed to respond to a request to denounce the invasion.

And Russian soprano Anna Netrebko said she was stepping back from performing amid controversy over her pro-Kremlin stance, despite her condemnation of the invasion. 

The Cannes Film Festival meanwhile banned Russian delegations from this year's event.