JP Morgan Chase, Deutsche Bank and Barclays will have to face questions from a joint probe by New York and Connecticut investigators after receiving subpoenas in recent weeks.
Britain’s RBS and HSBC have also been called to provide evidence, while UBS and Citigroup received similar demands earlier in the year.
The subpoenas request copies of communication between executives related to possible collusion and other conduct that may have played a role in alleged rate manipulation, a person familiar with the matter said.
Spokesmen for the US prosecutors declined to comment on the report.
The scandal shows no sign of going away with multiple investigations on both sides of the Atlantic. Martin Wheatley, the head of the Financial Services Authority, is carrying out an urgent review of Libor for the government and will report back next month.
In June Barclays, the first bank to admit it manipulated the benchmark interest rate, was fined £290m by US and UK authorities.