GENEVA (Reuters) - International mediator Lakhdar Brahimi began talks in Geneva on Friday with senior U.S. and Russian officials on seeking a political solution to the Syrian crisis.

Brahimi, Russian Deputy Foreign Minister Mikhail Bogdanov and U.S. Deputy Secretary of State William Burns - whose governments back different sides in the 21-month war - gathered at the United Nations European headquarters. None made any comment upon arrival of the closed-door talks.

Syria denounced Brahimi as "flagrantly biased" on Thursday, casting doubt on how long the U.N.-Arab League mediator can pursue his peace mission.

(Reporting by Stephanie Nebehay; Editing by Janet Lawrence)