JAKARTA: Indonesia's foreign exchange reserves slipped around $400 million in August to $117.9 billion, Bank Indonesia (BI) said on Friday, partly because of central bank intervention to defend the rupiah.

The rupiah has lost around 9 percent of its value so far this year. The currency was trading around its weakest levels in 20 years this week, closing at 14,815 per dollar on Friday.

The end-August reserves level, sufficient to meet 6.8 months of imports, "remained adequate as they will be supported by our confidence in stability, better economic prospect and positive export performance", the central bank said in a statement.

From February until August, the reserves had declined $14.1 billion.