SAO PAULO, Nov 27 (Reuters) - Brazil's central bank offered to buy dollars on the spot foreign exchange market on Friday in an ongoing effort to boost international reserves and soak up greenbacks pouring into the economy.

The bank has bought about $23 billion on the spot market since May 8, including about $1.988 billion this month through Nov. 20, to soak up dollar liquidity and prevent further appreciation of Brazil's currency, the real.

The currency (BRBY) was trading 0.34 percent stronger at 1.744 per U.S. dollar shortly after the central bank's announcement. (Reporting by Silvio Cascione; Writing by Luciana Lopez) ((luciana.f.lopez@thomsonreuters.com; Reuters Messaging: luciana.f.lopez.thomsonreuters.com@reuters.net; Tel: +5511-5644-7756))