BEIJING - China's yuan funds outstanding for foreign exchange fell for a 13th straight month in August, central bank data showed Thursday.

The funds stood at 21.2 trillion yuan ($3 trillion) at the end of last month, down by 8.4 billion yuan from July, according to a statement on the website of the People's Bank of China.

As the Chinese yuan is not freely convertible under the capital account, the central bank has to purchase foreign currency generated by trade surplus and foreign investment in the country, adding funds to the money market.

Such funds are an important indicator of cross-border foreign capital flows and domestic yuan liquidity.

A similar measure of capital flow, the country's foreign exchange reserves rose to $3.11 trillion at the end of August, up 1.1 percent from the start of the year, according to the State Administration of Foreign Exchange.