NEW YORK (Reuters) - The U.S. Federal Bureau of Investigation is working quickly to figure out who perpetrated the cyber heist of $81 million from Bangladesh Bank's account at the Federal Reserve Bank of New York in February, but there are no definitive answers yet, a top FBI official said on Thursday.

"We don't have a definitive answer to that question in terms of exactly who. There are a number of different tentacles to that, that we are looking at. And we're working as fast as we can to get a resolution," said Richard Jacobs, assistant special agent in charge of the cyber branch at the FBI's New York office.

(Reporting by Jonathan Spicer)