Yulia Navalnaya, the widow of deceased Kremlin foe Alexei Navalny, has urged on the West not to recognise the results of the presidential election, which starts on Friday.

"We know, given the track record of how votes are being prepared and organised in Russia under the current Kremlin administration and regime, how this will look like," said European Union spokesman Peter Stano.

"It's very difficult to foresee that this would be a free, fair and democratic election where the Russian people would really have a choice."

NATO secretary general Jens Stoltenberg also said the ballot "in Russia will not be free and fair".

"We know already that opposition politicians are in jail, some are killed, and many are in exile, and actually also some who tried to register as candidates have been denied that right," he said.

"There is no free and independent press in Russia."

The three-day vote, expected to result in President Putin claiming another six years in power, comes after his invasion of Ukraine has destroyed ties between Moscow and the West.

Both the EU and NATO condemned Russia's decision to stage the vote in areas of Ukraine that are occupied by its soldiers and that Moscow claims as its own territory.

"Russia's attempts to organise any part of an election in occupied regions of Ukraine are completely illegal, violating international law," Stoltenberg said.

EU spokesman Stano said the ballot in those regions "is not being recognised and it will not be recognised by the European Union".

Victory in the March 15-17 contest will allow Putin to stay in the Kremlin until at least 2030, longer than any Russian leader since Catherine the Great in the 18th century.

No genuine opposition candidate has been allowed onto the ballot.

Putin officially faces off against three Kremlin-approved candidates from political parties loyal to him and his policies.