The European Commission seized documents from several major banks yesterday, marking the escalation of a worldwide law-enforcement probe into how key interest rates are set, according to people familiar with the matter.

European officials are scrutinising an interest rate called the Euro Interbank Offered Rate, or Euribor, people familiar with the situation said. Euribor, set by more than 40 banks, is a benchmark used to determine interest rates on trillions of euros worth of euro-denominated loans and debt instruments.