Russia will suspend electricity supplies to Finland this weekend, a supplier said on Friday as tensions rise over Helsinki's NATO bid following the conflict in Ukraine.

"We are forced to suspend the electricity import starting from May 14," said RAO Nordic, a subsidiary of Russian state energy holding Inter RAO that sells its electricity on the Nordic market.

It blamed the suspension on not having received payment for electricity sold in May and said as a consequence it was no longer able to pay for more electricity from Russia.

"This situation is exceptional and happened for the first time in over 20 years of our trading history," RAO Nordic said, hoping the situation would "soon" improve and the trade could resume.

The Finnish electricity network operator said it would be able to make do without Russian electricity.

"We're prepared for this and it won't be difficult. We can make do with a bit more imports from Sweden and Norway," Fingrid's manager for operational planning Timo Kaukonen told AFP.

He said a little less than 10% of electricity consumed in Finland comes from Russia.

The announcement of the cut in electricity supplies came one day after Finland's leaders declared their nation must apply to join NATO "without delay" — a seismic change in policy since Russian President Vladimir Putin sent troops to Ukraine on Feb. 24.

The Kremlin has warned Russia would "definitely" see Finnish membership as a threat, while the Russian foreign ministry said Moscow would be "forced to take reciprocal steps, military-technical and other, to address the resulting threats," The Moscow Times reports.