DUBAI (Reuters) - Saudi Arabia’s central bank, which serves as the kingdom’s sovereign wealth fund, reported a fall of $6 billion in net foreign assets in March as low oil prices took their toll.

Net foreign assets held by the central bank dropped by 1.0 percent from the previous month to 2.17 trillion riyals ($579 billion) in March, central bank data showed on Thursday.

Assets fell 16.2 percent from a year earlier to their lowest level since April 2012. They reached a record high of $737 billion in August 2014 before starting to shrink. The central bank has been drawing down its assets to cover a huge state budget deficit caused by low oil prices.

The foreign assets are mainly denominated in U.S. dollars, in the form of securities such as U.S. Treasury bonds and deposits with banks abroad, fund industry sources and foreign banking sources told Reuters.

Equities account for a small fraction, perhaps under 20 percent, the sources said. Some of the Saudi assets are managed via global fund firms.

Deposits with banks abroad edged down 0.4 percent from the previous month to $132 billion in March, while investment in foreign securities fell 1.4 percent to $389 billion. The central bank does not provide a more detailed breakdown of its assets.

(Story corrects month in last paragraph to March from February).