Vietnam is buying the Su-30 fighters, at a time when disputes over sovereignty in the South China Sea are increasing. Vietnam has said it views the disputes with concern.

'Last week a contract was signed for the delivery to Vietnam of 12 Su-30MK2 in 2011-2012,' the news agency quoted a'military-diplomatic source' as saying.

According to the aircraft maker Sukhoi, the Su-30MK2 is designed for ground attacks and 'to gain air superiority through killing hostile manned and unmanned aircraft with guided missiles in medium-range engagements and dogfights'.

Vietnam, China and other countries have longstanding competing claims of sovereignty over parts of the South China Sea, which Vietnam calls the East Sea, including the potentially oil and gas-rich Spratly and Paracel island chains.

Previous arms deals, including the sale of six submarines, were announced when Vietnam's Prime Minister Nguyen Tan Dung visited Moscow last December, when the fighter deal also was discussed. -- REUTERS