MONROVIA (Reuters) - A grand jury in Liberia indicted on Thursday the chief executive officer of the London AIM-listed Sable Mining, Andrew Groves, in connection with an alleged bribery scandal involving several senior Liberian officials, the head of a special task force said.

President Ellen Johnson Sirleaf ordered in May an inquiry into Sable's attempt to acquire an iron ore concession in northern Liberia after the watchdog group Global Witness made accusations of wrong-doing in a report.

Also on Thursday a grand jury indicted a former head of the national investment commission of Liberia, Richard Tolbert.

Groves and Tolbert "are to be arrested and brought to this jurisdiction wherever they can be found", Fonati Koffa, head of the special taskforce set up by Sirleaf, said during a press conference in Monrovia.

Four people, including Parliament speaker Alex Tyler, chairman of Sirleaf's Unity Party Varney Sherman and deputy minister of Lands, Mines and Energy Ernest C.B. Jones, were indicted last month in that case along with Sable Mining.

They are accused of having used their positions to amend Liberia's public procurement and concessions law.

The prosecution said on Thursday there was not enough evidence yet to indict former Sable Mining chairman Phil Edmonds, but said it believed it would be the case soon.

"All that it takes to get all of those involved in criminality in our country, including getting them through Interpol and or extradition, will be considered", Darkue Mulbah, the lead prosecutor for the government said.

Sable Mining said last month that it had noted "the recent media comment and speculation regarding allegations of bribery and corruption" made against the company and said it was investigating these matters.

(Reporting by James Giahyue, Editing by Marine Pennetier)