ABU DHABI - First Abu Dhabi Bank, the United Arab Emirates' biggest lender, on Monday denied that it had tried to manipulate the Qatari riyal.

"FAB conducts its business in accordance with the highest professional standards and complies with the laws and regulations of the jurisdictions in which it operates. FAB categorically refutes these rumours," it said in a statement.

Letters seen by Reuters showed a law firm working for the central bank of Qatar asked U.S. regulators to investigate FAB's U.S. subsidiary, accusing it of "bogus" foreign exchange deals designed to harm Qatar's economy as part of a boycott of Doha by other Gulf states.

(Reporting by Stanley Carvalho; Editing by Andrew Torchia) ((stanley.carvalho@thomsonreuters.com; + 9712 6444431; Reuters Messaging: stanley.carvalho.thomsonreuters.com@reuters.net))