The dollar's share of known global currency reserves slipped in the third quarter, while total central bank holdings hit a record $9 trillion, International Monetary Fund data showed on Thursday.

Between July and September, the U.S. dollar's share of the roughly $5 trillion of world reserves of which the composition is known fell to 61.3 percent from 62.1 percent in the prior quarter.

Overall reserve accumulation rose for a sixth straight quarter, soaring to a record $9 trillion as of September 30. The composition of roughly $3 trillion of that is unknown but thought to be heavily concentrated in U.S. dollars.

The euro saw a modest boost in its share of known reserves to 26.9 percent from 26.5 percent and the yen's share rose to 3.6 percent from 3.3 percent.

Central banks have long been underweight the yen in their reserve portfolios. For more, see

The share of other currencies, which excludes the dollar, euro, yen, sterling and Swiss franc, rose to 4 percent from 3.8 percent in the second quarter of 2010.

Interest has grown in currencies such as the Australian and Canadian dollars, which have risen in value this year along with commodity prices, and some central banks have talked of increasing allocation to these currencies as well as the yen.

In the third quarter of 2009, the share of other currencies in known global reserves stood at 2.9 percent.

Valuation effects were also responsible for some of the allocation shift; the U.S. dollar lost more than 11 percent against the euro and about 5.5 percent against the yen in the third quarter of this year.

Worries about a euro-zone sovereign debt crisis eased in the third quarter, resurfacing only in November, while falling U.S. bond yields pushed the dollar down against the yen.

(Editing by Padraic Cassidy)