Banks approved for foreign exchange (forex) transactions in China bought more foreign currency than they sold in August, data from the nation's top forex regulator showed on Tuesday.

Chinese banks returned to a surplus in forex transactions after recording a deficit for two months in June and July, according to the State Administration of Foreign Exchange.

Banks purchased forex worth 147.9 billion U.S. dollars last month while selling a total of 139.5 billion U.S. dollars, creating a surplus of 8.3 billion U.S. dollars.

Foreign exchange transactions are a major cause of fluctuation in China's foreign exchange reserves, and the August surplus indicates a slowing outflow of foreign capital.

In the Jan.-Aug. period, forex purchases stood at 1.21 trillion U.S. dollars, with sales of 1.07 trillion U.S. dollars, a surplus of 139.8 billion U.S. dollars.