A satellite image collected over Ivankiv shows a Russian military convoy passing through northwest of Kyiv. Reuters

A 40-mile convoy of Russian tanks and other vehicles threatened Ukraine's capital on Tuesday as an intense shelling attack targeted the country's second-largest city, and both sides looked to resume talks in the coming days aimed at stopping the fighting.

A huge Russian military convoy was massing on the outskirts of Kyiv as fears grew the invading forces were set to launch devastating assaults aimed at taking control of Kyiv and other major cities.

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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.

The country's embattled president said he believed the stepped-up shelling was designed to force him into concessions.

A charred military vehicle is seen on a road near the town of Bucha in the Kyiv region, Ukraine. Reuters

"I believe Russia is trying to put pressure (on Ukraine) with this simple method," Ukrainian President Volodymyr Zelenskyy said late Monday in a video address. He did not offer details of hourslong talks that took place Monday, but he said Kyiv was not prepared to make concessions "when one side is hitting another with rocket artillery.”

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.

A view shows a destroyed bridge near the town of Bucha in the Kyiv region, Ukraine. Reuters

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".

An ambulance is seen through the damaged window of a vehicle hit by bullets in Kyiv, Ukraine. Reuters

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

The developments came as Russia finds itself increasingly isolated as a result of international condemnation and potentially backbreaking economic sanctions. Five days into the invasion, the Russian military's movements have been stalled by fierce resistance on the ground and a surprising inability to dominate the airspace.

The Kremlin has twice in as many days raised the specter of nuclear war and put on high alert an arsenal including intercontinental ballistic missiles and long-range bombers. Stepping up his rhetoric, President Vladimir Putin denounced the U.S. and its allies as an "empire of lies.”

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.

A charred armoured vehicle is seen on a street in the town of Bucha in the Kyiv region, Ukraine. Reuters

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."