Icap was tight-lipped after fresh allegations emerged linking it to investigations by regulators into the manipulation of interest rates.
The inter-dealer broker, led by Michael Spencer, is already in the sights of the Financial Services Authority, which is investigating Libor rate rigging.
It was reported that the US futures regulator has issued subpoenas to Icap and several large banks about the ISDAfix benchmark, an interest rate swap mechanism run from New York.
The investigation by the Commodity Futures Trading Commission marks a widening of the global investigation into alleged rate rigging.
In a short statement Icap, which acts as a middleman for trades between banks, clarified that while it is "involved in the administration" of ISDAfix, it does not make submissions on what the rate should be.
The statement added: "Icap had no knowledge of the allegations prior to the media speculation and is investigating them. Until those investigations are complete it will not make any further comment."
Mr Spencer has sought to play down his firm's role in Libor, saying initially that the investigations were not a "high concern".
He later added: "I am shocked, disappointed and saddened at the revelations that have emerged about Libor in recent months … if we determine that there has been any wrongdoing by any of our employees we will not hesitate to take extremely firm action against them."
UBS and Barclays have paid large fines to settle Libor fixing inquiries.