NEW YORK (BLOOMBERG) - In the days after the Ukraine war began, the rouble's collapse was a potent symbol of Russia's new-found financial isolation.

International sanctions on President Vladimir Putin's regime sank it to a record low of 121.5 roubles per US dollar, triggering memories of the battering it took during the 1998 Russian financial crisis.

Things looked dire enough that United States President Joe Biden said the rouble had been reduced to "rubble".

Now, though, it sure has not. The rouble has surged all the way back to where it was before Mr Putin invaded Ukraine, closing at 79.7 in Moscow on Wednesday (April 6).

What has become clear is that despite an incredibly wide-ranging package of sanctions on the Russian government and its oligarchs, and an exodus of foreign businesses, the actions are largely toothless if foreigners keep guzzling Russian oil and natural gas - supporting the rouble by stocking Mr Putin's coffers.

Even as Russia remains mostly cut off otherwise from the global economy, Bloomberg Economics expects the country to earn nearly US$321 billion (S$436.7 billion) from energy exports this year, up more than a third from 2021.

The rapid rouble recovery gives Mr Putin a major victory back in Russia, where many people fixate on the currency's ups and downs, even as his military gets bogged down in Ukraine and outrage mounts across the globe over atrocities it has committed.

"For the politicians, it is a good PR tool by saying that sanctions don't have any impact. And it will help to limit the inflation impact," said Mr Guillaume Tresca, a senior emerging-market strategist at Generali Insurance Asset Management.

In Russia's post-Soviet history, the rouble-dollar exchange rate has arguably been the economic indicator that Russians care most about. The rate was broadcast by the exchange kiosks that sprung up in every town and city, flagging the currency's collapse as hyperinflation erupted in the early 1990s. The rouble dived again after Russia defaulted in 1998.

Once that chaos subsided, the government lopped off three zeros. Then during the 2008 crisis, the authorities burned through billions of dollars to slow the currency's slide, in part to avoid spooking the population and sparking a run on the nation's banks. Central bank governor Elvira Nabiullina decided to risk that in 2014 when sanctions over the Crimea annexation and slumping oil prompted her to switch the currency to a free float.

In response to this year's sanctions, Russia has enacted capital controls that also appear to be supporting the rouble. This includes freezing the assets held by non-resident investors, and telling Russian companies to convert 80 per cent of the foreign currencies they hold into roubles.

This has some observers doubting the significance of the rouble's recovery to pre-invasion levels - which is also happening amid the lightest trading volume in a decade.

"It is not a free-floating currency given all the measures imposed by the authorities," Mr Tresca said.

US Treasury Secretary Janet Yellen said basically the same thing on Wednesday when testifying before Congress, warning against drawing deeper messages about sanctions from the rouble's rebound.

Still, it is hard to ignore the lifeline other nations are tossing Mr Putin by buying his country's oil and gas. Doing so gives Russia a current account surplus - economics jargon for exporting more than you import, which tends to lift a the country's currency - and undermines the attempt to pummel Russia with sanctions.

Russia has been able to stabilise local markets and even stave off a messy foreign default - at least for now. This means that if the coalition of governments that oppose Mr Putin wants to hurt the rouble again, it will likely have to change tack. Just this week, the US Treasury barred US dollar debt payments from Russian accounts at American banks, an attempt to make Russia drain its domestic dollar reserves or default.

Economists pointed to the likelihood of more tightening of financial sanctions, perhaps even disconnecting additional Russian institutions from Swift, the communications system banks use to move money around the world.