KYIV (AFP) -- A huge Russian military convoy was massing on the outskirts of Ukraine's capital Tuesday as fears grew the invading forces were set to launch devastating assaults aimed at taking control of Kyiv and other major cities.

Satellite images showed a long build-up of armoured vehicles and artillery starting 29 kilometres (18 miles) north of the city, as Moscow defied mounting global pressure and a wave of international sanctions that have smashed Russia's economy.

Initial ceasefire talks between Moscow and Kyiv on Monday failed to secure a breakthrough, with Russia shelling residential areas in Ukraine's second city Kharkiv and other areas of the country after the negotiations.

The Russian army has been regrouping and massing its forces over the past 24 hours "primarily to encircle and take control of Kyiv and other major cities," the general staff of Ukraine's armed forces wrote on Facebook.

The column is more than 65 kilometres long and covers the entire road from near Antonov airport outside Kyiv to the town of Prybirsk, US satellite imaging company Maxar said.

"Some vehicles are spaced fairly far apart while in other sections military equipment and units are traveling two or three vehicles abreast on the road," Maxar said.

The images also showed "additional ground forces deployments and ground attack helicopter units" in southern Belarus near the Ukraine border.

Eastern city Kharkiv's mayor Igor Terekhov, quoted by Ukrainian media, warned that Moscow's armoured vehicles and tanks are "everywhere around the city".

Russian forces killed several civilians including children late Monday, he said.

The mayor of Kherson, Igor Kolykhayev, also wrote on Facebook that the Russian army had set up checkpoints at all of the city's entrances, but said it "remains Ukrainian" and "will be able to resist".

Explosions were also reported in and around Brovary, a city on the outskirts of the capital.

In Kyiv, many were preparing for a fresh assault with makeshift barricades dotting the streets.

"We will greet them with Molotov cocktails and bullets to the head," bank employee Viktor Rudnichenko told AFP. "The only flowers they might get from us will be for their grave."

More than 350 civilians, including 14 children, have been killed since the invasion last Thursday, Ukraine says, while more than half a million people have fled the country.

Moscow claimed Monday it had "gained air superiority over the entire territory of Ukraine".

Ukrainian President Volodymyr Zelensky called for a global ban on Russian planes and ships entering the world's airports and seaports in a bid to stem Moscow's assault.  

Russian President Vladimir Putin announced his demands to bring the war to an end in a phone call with his French counterpart Emmanuel Macron on Monday.

They included recognition of Russian sovereignty over Crimea and Ukraine's demilitarisation.

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

The weekend featured a momentous series of announcements from Europe, with Germany unveiling a historic change to its defence policies.

The EU also said it would buy and supply arms to Ukraine, the first such move in its history.

Moscow came under fire on Monday at the UN General Assembly and the International Criminal Court (ICC), which opened a war crimes investigation.

"I am satisfied that there is a reasonable basis to believe that both alleged war crimes and crimes against humanity have been committed in Ukraine"

since 2014, ICC prosecutor Karim Khan said in a statement.

Russia also faced urgent calls at an extraordinary UN General Assembly debate to end its "unprovoked" and "unjustified" assault.

Inside the General Assembly hall Monday, UN Secretary-General Antonio Guterres pleaded: "The fighting in Ukraine must stop. Enough is enough."

The United States expelled 12 members of Moscow's UN mission from America on Monday for being "intelligence operatives".

Canada announced a ban on Russian oil imports Monday.

The European Union and its allies were also preparing more sanctions against Russia in the coming days to "raise the cost" of war in Ukraine, an aide to Macron told reporters.

And 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.

The Russian ruble crashed to a record low as sanctions imposed by the West over the weekend had an immediate impact in Moscow, forcing the central bank to more than double its key interest rate to 20 percent.

Putin also announced emergency measures intended to prop up the ruble, including banning residents from transferring money abroad.

Many Russians raced to withdraw cash.

Retired soldier Edward Sysoyev, 51, fidgeted impatiently while in line at a bank in Moscow.

"Ninety percent of Russians are going to rush to withdraw their rubles and change them into dollars, property or even gold... it'll be ordinary people who pay for this military bun-fight," he said. 

The response from the world of sports also gathered steam, as Russia was expelled from the World Cup and the country's clubs and national teams were suspended from all international football competitions "until further notice", FIFA and UEFA said.

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

Authorities in badminton, rugby, ice hockey, basketball and Formula One have all moved to act against Russia, either banning Russian national teams and clubs, or suspending events in Russia.

The growing sporting isolation comes as hundreds of thousands flee their homes west into Europe after the Russian invasion.

More than half a million people have already fled abroad, the UN refugee agency said Monday, with neighbouring Poland alone having taken in nearly 300,000 people.

Many more are expected to follow.

Iryna Plakhuta, a pregnant 43-year-old executive, had to leave her family behind in the capital because of fears over her safety.

"Our husbands stayed in Kyiv," she said. "They are protecting Ukraine. It's so hard." (AFP)