Britain's Serious Fraud Office (SFO) has launched an investigation into Glencore over suspicions of bribery, it said on Thursday, adding to the legal woes of one of the world's biggest commodity traders.

Since July last year, Glencore has been subject to a U.S. Department of Justice enquiry in connection with corruption in the Democratic Republic of Congo, Venezuela and Nigeria.

Britain's SFO on Thursday said it was also investigating the conduct of Glencore businesses, its officials, employees, agents and associated persons, without commenting further.

Glencore, which has operations in over 150 countries, said it would cooperate with the investigation.

The company's shares were trading 7% lower at 221.60 pence by 1439 GMT, the biggest decline among London's blue-chip stocks .

Over the course of this year, Glencore's shares have fallen more than 20%, pressured by broader concerns about safety and sustainability in the Democratic Republic of Congo.

CEO Ivan Glasenberg told investors earlier this week he expected to step down next year once a new management team is in place.

Analyst Paul Gait at Bernstein said the SFO action would inevitably add to Glencore's problems, but it was not yet clear whether it was "genuinely incremental or just the SFO piggybacking on the DoJ."