* Scope of SFO investigation is unclear
* DoJ is already investigating Glencore
* Share price down 9% to 3-year low
* Law firm plans legal action on behalf of investors (Adds comments from sources, share price, lawsuit, dateline)
By Yadarisa Shabong, Julia Payne and Kirstin Ridley
LONDON, Dec 5 (Reuters) - The UK's Serious Fraud Office (SFO) has launched a bribery investigation into Glencore , adding to legal troubles that have hit the shares of one of the world's biggest miners and commodity traders.
The SFO said on Thursday it had opened an investigaton into suspicions of bribery in the conduct of business by the Glencore group of companies, its officials, employees, agents and associated persons in June. It declined to comment on the scope of its inquiry.
The London-listed shares of Glencore, which has operations in over 150 countries, fell 9% to 216.9 pence, their lowest level in more than three years, knocking 2.6 billion pounds ($3.3 billion) off the company's market value.
Glencore, which was subpoenaed in July 2018 by the U.S. Department of Justice over possible violations of the Foreign Corrupt Practices Act relating to operations in Nigeria, Venezuela and the Democratic Republic of Congo (DRC), said it would cooperate with the investigation.
Two sources familiar with the matter said the SFO had recently sought information relating to Glencore's involvement in the DRC and its former business partner, Israeli billionaire businessman Dan Gertler.
Reuters was unable to ascertain whether those enquiries were part of the SFO's bribery probe.
A London-based spokesman for Gertler declined to comment.
Gertler was sanctioned by the United States in 2017 over allegations he used his friendship with former DRC President Joseph Kabila to secure sweetheart mining deals. He denied all allegations of impropriety at the time.
Over the course of this year, Glencore's shares have fallen more than 20%, pressured by broader concerns about safety and sustainability in the DRC. Canada's regulatory authorities fined a Glencore-controlled subsidiary last year after allegations of inadequate financial disclosures in the DRC.
The legal difficulties have upset shareholders. Boies Schiller Flexner, a London-based law firm, said it was mounting a fully-funded legal action on behalf of institutional investors against Glencore for damages that could exceed 1.0 billion pounds.
Glencore's CEO Ivan Glasenberg told investors earlier this week he expected to step down next year once a new management team is in place.
The investigation is one of the most high-profile SFO probes launched under Lisa Osofsky, a former FBI lawyer appointed director last August, who has come under fire for abandoning some of the agency's most prominent and lengthy probes.
The SFO dropped its investigations into aero engine maker Rolls-Royce and drugs maker GlaxoSmithKline in February and ended a seven-year, Libor benchmark interest rate inquiry in February.
($1 = 0.7794 pounds)
(Additional reporting by Yadarisa Shabong in Bengaluru; Alistair Smout, Barbara Lewis and Zandi Shabalala in London; Editing by Jane Merriman and Elaine Hardcastle)