China is to buy a batch of 24 Sukhoi-35 fighter jets from Russia in a deal worth more than $2 billion, an industry source told Reuters on Thursday, in a move that may help the Kremlin's strained finances.

A spokeswoman for Russian state holding Rostec confirmed a deal between the two countries had been signed involving Su-35 fighter jets, but declined to provide details.

The deal makes China the first foreign buyer of the Su-35, one of Russia's most advanced military aircraft, and is one of the largest contracts for military jets to have ever been signed between the two countries.

Russia and China have been in talks for several years over the Su-35s, and in 2012 the two sides signed a preliminary agreement for Beijing to buy some of the jets, the Kommersant newspaper reported.

Arms sales are a rare bright spot in an otherwise gloomy economic picture for Russia, whose economy is suffering from weak oil prices and Western sanctions over the Ukraine conflict.

Moscow has sought to deepen trade and financial ties with Beijing following the chill in relations with the West over Ukraine, but some analysts are skeptical as to whether the drive has yielded much in the way of early results.

It is not clear when China will pay Russia the more than $2 billion fee for the Su-35 jets.