Russia’s Gazprom Neft, the oil arm of top global gas producer Gazprom, said on Monday it planned to purchase 49 percent of the operator of Vietnam’s Dung Quat refinery, the country’s sole oil processing facility.

It has also agreed to step up cooperation in the broader energy sector by expanding oil and gas exploration and production in Vietnam with state oil firm PetroVietnam.

Energy cooperation has long been a feature of the relationship between Vietnam and Russia, starting with the constructions in Vietnam of hydro power plants in the 1980s, followed by an oil and gas joint venture Vietsovpetro and, most recently, the development of nuclear energy.

Gazprom Neft said in a statement it now had exclusive rights to negotiate with state oil and gas group PetroVietnam on acquiring 49 percent of the shares -- the foreign ownership ceiling in a Vietnamese company -- in Binh Son Refining and Petrochemical Co, the refinery operator.

The statement gave no value or timing for the purchase.

Dung Quat refinery has said it would process 8.5 million tonnes of crude oil a year (171,000 barrels per day) once a projected upgrade is finished by 2022.

Gazprom Neft and PetroVietnam signed a memorandum on Monday to extend collaboration on joint oil and gas exploration, production and development projects on the Pechora Sea shelf northwest of Russia, the statement said.

By October 2015 the two will release a list of priority oil and gas fields and agree the basic terms of the partnership.

The signing on Monday was witnessed by visiting Russian Prime Minister Dmitry Medvedev and his counterpart Nguyen Tan Dung.

Vietsovpetro produces about one third of Vietnam’s crude oil output. Russia is currently helping train Vietnamese staff for the country’s first nuclear power plant, with construction slated to begin in 2020.