Interdealer broker Tullett Prebon has suffered a network outage that has hit users of one of its voice broking businesses.
The downtime occurred at 4.50pm Thursday and has yet to be resolved.
"As of 7am GMT today, significant progress has been made in diagnosing the problem and initiating recovery," the company says in a statement. "It is a network outage and not a cyber-attack."
Tullett states that transactions in flight when the lights went down have been "identified and managed accordingly".
The company says that it has reported the incident to regulatory bodies and is working with its network and hardware providers to resolve the issue.
"The organisation is fully mobilised and working on this as a matter of urgency," states Tullett. "We hope to have the issue resolved during the course of today.