SILVER SPRING, Md. (Reuters) - U.S. Democratic presidential hopeful Hillary Clinton on Thursday said she always put U.S. interests first when she was secretary of state, following a report that her family's foundation benefited after she helped a Swiss bank in a U.S. tax case.

The Wall Street Journal said that while Clinton was in office, she intervened on behalf of UBS AG. The bank then increased its donations to the Clinton Foundation, her family's charitable organization, the paper said.

On Thursday, Clinton said she did nothing improper. "This is just the kind of unfortunate claim or charge that you see in campaigns, and all I can do is tell you there is no basis to it," she told reporters.

(Reporting by Megan Cassella; Writing by Emily Stephenson; Editing by Sandra Maler)