WASHINGTON, United States - US President Joe Biden announced "devastating" Western sanctions against Russia on Thursday and was shortly to address the American people on the unfolding invasion of Ukraine.

After a virtual, closed-door meeting which lasted an hour and 10 minutes, the group of rich Western democracies -- Britain, Canada, France, Germany, Italy, Japan and the United States -- said it was standing firm against Russia's "threat to the rules-based international order."

Biden tweeted that the G7 leaders "agreed to move forward on devastating packages of sanctions and other economic measures to hold Russia to account. We stand with the brave people of Ukraine."

In a joint statement, the seven industrial powers also said they were "ready to act" to minimize disruptions to world energy markets as a result of Moscow's assault on Ukraine and with sanctions already targeting a major pipeline from heavyweight energy producer Russia.

Before the G7 gathering, Biden first huddled with his National Security Council in the Situation Room, the White House said. His speech to the nation was scheduled for 13:30 pm (1830 GMT), after being delayed by an hour.

For weeks, as Russia built up tens of thousands of troops and heavy weapons on Ukraine's border, Biden has led NATO and other European allies in trying to craft a package of what Washington says are "unprecedented" sanctions as a deterrent.

Now that deterrence has failed, Western countries are moving to punish Russia.

US officials are teeing up new sanctions that could include targeting huge banks, more oligarchs close to Putin and, crucially, a ban on exports to Russia of high-tech equipment and components.

It was not clear how many of these measures would be announced Thursday by Biden. But in London, Prime Minister Boris Johnson said Britain is freezing the UK assets of Russian titans in banking and arms manufacturing, sanctioning five more oligarchs, and banning Aeroflot.

And Germany's vice chancellor, Robert Habeck, signalled Thursday there would be a "strong sanctions package" that will "cut off the Russian economy from industrial progress, will attack and freeze assets and financial holdings, and will dramatically limit access to the European and American markets."

- Next step -

A first round of Western sanctions was unleashed Tuesday, after Putin announced he would send troops as "peacekeepers" to two small areas already controlled by Moscow-backed separatists.

The US government joined European allies in imposing sanctions on two Russian banks, Moscow's sovereign debt, several oligarchs and other measures.

Then on Wednesday, as the Russian invasion force became clearly primed to attack, Biden announced he was imposing sanctions on the Nord Stream 2 natural gas pipeline from Russia to Germany -- one of Moscow's highest-profile geopolitical projects.

Germany had earlier announced it would block the pipeline from opening for deliveries.

US State Department spokesman Ned Price warned this week that "no Russian financial institution is safe."

But some measures risk serious economic fallout for Western countries and could imperil the global economy recovery after the Covid pandemic. Already stock markets are tumbling and oil prices are soaring over $100 a barrel.

Among the more controversial sanctions would be directly targeting Putin, who is widely reported to have amassed a vast, secret fortune during his two decades running Russia.

Arguably the highest stakes sanction would be cutting Moscow off from the SWIFT international banking network. This would at least for some time disconnect Russia from basic commerce, hugely disrupting the economy, but it would also carry considerable potential aftershocks to the wider, US-led financial system.

Ukrainian President Volodymyr Zelensky, speaking Thursday as Russian troops broadened their attack on his country, appealed directly for Moscow to be yanked from SWIFT.