INTERNATIONAL: Talks between Russian and Ukrainian officials began on the Belarusian border on Monday, Moscow has said, as Russia's diplomatic and economic isolation deepens four days after invading Ukraine, the biggest assault on a European state since World War Two.

Russian forces seized two small cities in southeastern Ukraine and the area around a nuclear power plant, the Interfax news agency said on Monday, but ran into stiff resistance elsewhere.

Talks began with the aim of an immediate ceasefire and the withdrawal of Russian forces, the Ukrainian president's office has said, after a Russian advance that has gone more slowly than some expected.

Russia has been cagier, with the Kremlin declining to comment on Moscow's aim in negotiations.

It was not clear whether any progress could be achieved after President Vladimir Putin on Thursday has launched the assault and put Russia's nuclear deterrent on high alert on Sunday.

The talks are being held on the border with strong Russian ally Belarus, where a referendum on Sunday approved a new constitution ditching the country's non-nuclear status at a time when the former Soviet republic has become a launch pad for Russian troops invading Ukraine.

The Western-led response to the invasion was sweeping, with sanctions that effectively cut off Moscow's major financial institutions from successive Western markets sending Russia's rouble currency down 30 percent against the dollar on Monday. Countries also stepped up weapons supplies to Ukraine.

 President Volodymyr Zelenskyy calls the next 24 hours “crucial” for Ukraine.

Civilian death toll now stands at 352 people, including 14 children, Ukraine’s health ministry says.

Chelsea owner Roman Abramovich helps Ukraine negotiate for peace.

Russian billionaire Roman Abramovich, who owns England’s Chelsea Football Club, has accepted a Ukrainian request to help negotiate an end to the conflict between Russia and Ukraine, his spokeswoman says.