At least several European banks that vowed to stop doing business with Iran have kept handling billions of euros in transactions for Iranian entities and foreign companies with operations there, a review of regulatory filings and other documents by The Wall Street Journal shows.

The dealings aren't suspected of violating any sanctions, which are looser for the continent's banks under European Union rules than prohibitions imposed by the US. But some government officials and banking experts said the banks are risking embarrassment or regulatory problems in the US as it scrutinises financial transactions with sanctioned countries.