Olympics-U.S. swimmers damaged gas station, quarrelled with guards - source

RIO DE JANEIRO, Aug 18 (Reuters) - Four U.S. Olympic swimmers caused damage at a gasoline station and were involved in a dispute with guards who asked them to pay for the damage, a Brazilian security source said on Thursday, casting doubt on their story that they were robbed at gunpoint. A spokesperson for the U.S. Olympic Committee (USOC) declined to comment. The USOC said earlier on Thursday that three of the swimmers who remain in Brazil would be helping police with their investigation, after authorities stopped two of them leaving the country the previous day. The fourth swimmer, gold medallist Ryan Lochte, returned to the United States on Monday. (Reporting by Rodrigo Viga; Writing by Daniel Flynn; Editing by Mark Bendeich)