KYIV/MOSCOW. A huge Russian armoured column bore down on Kyiv on Tuesday, after the lethal shelling of civilian areas in Ukraine's second largest city raised fears that frustrated Russian commanders could resort to more devastating tactics.

Nearly a week since after Moscow launched war on its neighbour it has failed to capture a single major Ukrainian city after running into unexpectedly fierce resistance.

Western countries fear that Russian commanders could now unleash the tactics they employed in Syria and Chechnya in recent decades, when they pulverised civilian areas, killing thousands, as they sent in their tanks.

Oil company Shell became the latest Western firm to announce it was pulling out of Russia. International sanctions and global financial isolation have had a sudden and devastating impact on Russia's economy, with the rouble in freefall and queues outside banks as Russians rush to salvage their savings.

US satellite company Maxar released pictures showing tanks and fuel trucks snaking along a highway from the north, bearing down on Kyiv along 40 miles (60 km) of highway.

"For the enemy, Kyiv is the key target," President Volodymyr Zelenskiy, who has remained in the capital rallying Ukrainians with regular video updates, said in his latest message overnight. "We did not let them break the defence of the capital, and they send saboteurs to us ... We will neutralise them all."

Ukrainian authorities also reported 70 soldiers killed in a rocket attack in a town between Kyiv and Kharkiv.

"The Russian advance on Kyiv has made little progress over the past 24 hours probably as a result of continuing logistical difficulties," the British defence ministry said in a military intelligence update on Tuesday.

But it also warned of a shift in Russian tactics putting civilians in greater peril: "The use of heavy artillery in densely populated urban areas greatly increases the risk of civilian casualties."

The city that bore the brunt of the attack on Monday was Kharkiv, Ukraine's second-largest city, with 1.5 million people, located near the Russian border in eastern Ukraine. Officials say dozens of people were killed and injured on Monday by missile strikes that hit civilian areas.

"Barbaric rocket attacks and MLRS (multiple launch rocket systems) of peaceful cities are evidence that they are no longer able to fight armed Ukrainians," Ukrainian Defence Minister Oleksii Reznikov said on Facebook.

Human rights groups and Ukraine's ambassador to the United States accused Russia of using cluster bombs and vacuum bombs, weapons normally banned in civilian areas. The United States said it had no confirmation of their use.

Russia has not given a full account of its battlefield losses, but pictures from Ukraine have shown burnt-out Russian tanks and bodies on the road where they have been attacked by Ukrainian defenders.

Ukraine's general staff said Russian losses included 5,710 personnel, 29 destroyed and damaged aircraft and 198 tanks, all figures that could not be verified.

Ceasefire talks held on Monday at the Belarus border failed to reach a breakthrough. Negotiators have not said when a new round would take place.

Putin's Russia faces near total international isolation over his decision to launch what he called a "special military operation" to disarm Ukraine and capture "neo-Nazis and drug addicts" that lead it.

Most devastating for Russia have been sanctions on its central bank that prevent it from using its $630 billion foreign reserve war chest to prop up the rouble.

Turkey shuts straits to warships

NATO ally Turkey delivered another blow to Moscow on Monday by warning warring countries not to send warships through its Bosphorus and Dardanelles Straits that separate the Black Sea from the Mediterranean, effectively bottling up Russia's Black Sea Fleet.

Public health experts say Ukraine is running low on critical medical supplies and fears of a wider public health crisis are growing as people flee their homes and health services and supplies are interrupted.

More than 500,000 people have fled Ukraine, according to the United Nations refugee agency, setting off a refugee crisis as thousands await passage at European border crossings.

Oil companies Shell (SHEL.L), BP and Norway's Equinor (EQNR.OL) have said they would exit positions in Russia, which relies on oil and gas for export earnings.

Canada said it would ban imports of Russian crude oil, and US Republican Senator Lindsey Graham urged the Biden administration to target the Russian energy sector with sanctions.

"We're not using the energy sector as a weapon," Graham told reporters. "We're failing to hit Putin where it hurts the most."

Leading banks, airlines and automakers ended partnerships, halted shipments and called Russia's actions unacceptable.

Mastercard said it had blocked multiple financial institutions from its payment network as a result of sanctions on Russia and Visa (V.N) said it would take action too.

Three major studios, Sony, Disney and Warner Bros, said they would pause theatrical releases of upcoming films in Russia while FIFA and the International Olympic Committee moved to bar Russian teams and athletes from competing.

Putin, who takes pride in athleticism and is passionate about martial arts, had his honorary black belt from World Taekwondo stripped from him over the invasion, the group said.