Russia said on Tuesday it was launching a buyback offer on its $2 billion sovereign Eurobonds maturing on April 4, its biggest debt payment of the year, and would make full payment to bondholders taking up the offer in roubles.

The move follows ever tightening Western sanctions imposed on Russia over its invasion on Ukraine. Moscow has called the Western measures "economic war" and has also demanded that foreign companies now needed to pay for Russian gas in roubles.

Bondholders should submit requests to sell their holdings to the National Settlement Depository between 1300 GMT on March 29 to 1400 GMT on March 30, the finance ministry said in a statement.

The Eurobonds would be bought at a price equivalent to 100% of their nominal value, it said.

The bond has a 30-day grace period and no provisions for payments in alternative currencies, according to JPMorgan.

The finance ministry did not in Tuesday's statement say how much of the $2 billion in outstanding Eurobonds it planned to buy back or what its actions could be should bondholders refuse to accept the offer.

"Obligations under the bonds redeemed by the finance ministry will be recognised as fulfilled ahead of schedule," the ministry said, adding that it reserved the right to change the timing of the buyback.

The finance ministry had said earlier on Tuesday it had fully paid a $102 million coupon on Russia's Eurobond due in 2035, its third payout since Western sanctions called into question Moscow's ability to service foreign currency debt.

Russia's next payment is on March 31 when a $447 million payment falls due. On April 4, it also should pay $84 million in coupon a 2042 sovereign dollar bond .

(Reporting by Reuters; Editing by Edmund Blair)