BEIJING, Jan. 3 (Xinhua) -- China's yuan slightly gained against a basket of currencies in December, according to a China Foreign Exchange Trade System (CFETS) index.

The CFETS RMB Index, which measures the yuan's strength relative to a basket of currencies, came in at 94.85 at the end of last month.

This marked a 0.51 percent increase from a month earlier, CFETS said.

The index compares the yuan to the value of 24 currencies, including the U.S. dollar, euro and Japanese yen, which was expanded from a basket of 13 currencies in 2016.

In December, an index that measures the yuan against the Bank for International Settlements currency basket went up 0.74 percent to 95.93, while against the Special Drawing Rights basket it strengthened 0.84 percent to 95.99, according to CFETS.

The yuan's onshore exchange rate strengthened by 6.72 percent last year, the sharpest annual appreciation in nine years, according to calculations by financial information provider Eastmoney.

The currency's robust performance was the result of a weaker dollar, sound economic fundamentals, improved regulation on capital flows, a relatively tightened monetary environment and increased global use of the currency.