The United Arab Emirates' central bank failed to act on warnings about a local firm which was helping Iran to evade sanctions, the BBC has found.
Leaked documents show Dubai-based Gunes General Trading processed $142m (£110m) in suspicious transactions through the UAE financial system in 2011 and 2012.
The activity was flagged by a British bank, but the firm was able to continue using local financial institutions.
In 2016, the US said it was involved in a major sanctions-busting scheme.
The Central Bank of the UAE did not respond to the BBC's request for comment.
Gunes General Trading has been wound up within the last two years. The BBC has been unable to reach anyone for comment.
The documents - known as the FinCEN Files - were leaked to BuzzFeed News, then shared with the International Consortium of Investigative Journalists (ICIJ) and BBC News Arabic.