By Foo Yun Chee
BRUSSELS (Reuters) - UBS
The European Commission has been looking into the case for about a year as part of its investigation into the fixing of lending benchmarks.
The source said there were other banks involved. It was not immediately clear which other financial institutions were under investigation.
Commission spokesman for competition policy, Antoine Colombani, said: "Our investigation is ongoing. We have no further comment."
RBS, UBS and Credit Suisse declined to comment.
The EU competition watchdog imposed a record 1.7 billion euro fine on five banks - Deutsche Bank
(Additional reporting by Matt Scuffham in London and Clare Hutchison in Zurich, editing by Adrian Croft and David Evans)