Some European traders have started to pay Russia for gas sales in roubles, while large clients have yet to do so, two sources familiar with the matter told Reuters on Thursday.

"Several traders, maybe more than five, have started payments," one source said on condition of anonymity because they were not authorised to speak to the media.

Russian President Vladimir Putin has demanded that countries he terms "unfriendly" must pay for gas in roubles or be cut off.

Under the new Russian payment system, buyers are obliged to deposit euros or dollars into an account at Gazprombank, which has then to convert them into roubles, place the proceeds in another account owned by the foreign buyer and transfer the payment in Russian currency to Gazprom.

The scheme was designed as a response to sweeping Western sanctions against Russia following the start of what Moscow calls its "special military operation" in Ukraine.

Gazprom and Gazprombank did not respond to requests for comment on Thursday.

The European Commission has accused Moscow of blackmail over its demand to be paid in roubles but in an advisory note issued last week, the Commission said buyers of Russian gas could participate in the scheme if they could confirm payment was complete once they had deposited euros, as opposed to later when the euros were converted to roubles.

Russia cut off gas supplies to Poland and Bulgaria on Wednesday after they refused to pay in roubles under the new arrangement stipulated by Putin.

A senior European Union official said on Thursday that Poland and Bulgaria both used their existing method to pay for Russian gas before Moscow cut their gas supplies, and the countries did not comply with Moscow's proposed mechanism to pay in roubles.

The Kremlin has said payments for deliveries that took place after Putin's decree took effect were expected in May. A source named May 20 as "validation" date for payments.

There have been mixed signals from Gazprom's top consumers of gas about the rouble scheme of payments.

Three sources said on Thursday that Italian energy group Eni has yet to make a decision regarding the payment scheme Russia has introduced and is waiting for clarity on whether it amounts to a breach of sanctions.

Uniper, Germany's main importer of Russian gas, said on Monday it would be possible to pay for future supplies without breaching European Union sanctions. However, it later said that no decision had been made.

Hungary has said it plans to pay for Russian gas in euros through Gazprombank, which will convert the payment into roubles to meet the new requirement.

Reuters