Vietnam has signed a deal to buy 12 Russian Sukhoi Su-30 fighter jets from Russia for about $500 million, Russian media reported on Thursday, citing industry sources.

"A contract to deliver SU-30MK2 (jets) was signed by (state arms export monopoly) Rosoboron export at the start of the year," Interfax news agency quoted a defence industry source as saying.

Vedomosti business daily, citing two defence industry sources, said deliveries of the 12 supersonic jets would begin next year. Rosoboron export refused to comment on the report.

Experts polled by Vedomosti and Interfax estimated the contract would be worth between $500 million and $600 million.

The Su-30, known as "Flanker-C" to NATO, is a more formidable version of the Su-27. It made its first flight in the days of the Soviet Union but was introduced to service in post-communist Russia in 1996.

Vedomosti reported in April that Vietnam was in talks with Rosoboronexport to deliver six Project 636 Kilo-class diesel-powered submarines in a deal estimated by the business daily at $1.8 billion.

If that deal is secured, Vietnam would become one of Russia's top-five arms sales customers, Vedomosti reported.

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