South Korea’s foreign exchange reserves have tumbled for the third consecutive month in January due to the strengthening of the greenback against some European currencies.

The Bank of Korea(BOK) said Wednesday that foreign exchange reserves fell 670 million U.S. dollars from the previous month to 367-point-29 billion dollars in January.

It is the third straight month the country’s foreign reserves fell since the drop of one-point-14 billion dollars in November.

The central bank said although it managed to boost returns from investments using foreign reserves, some non-dollar currencies it held including the British pound, have fallen significantly in value. The BOK said this in turn caused contraction of the value of dollar-denominated foreign reserves.

As of December, South Korea had the seventh largest foreign reserves in the world following China, Japan, Saudi Arabia, Switzerland, Taiwan and Russia.