Moscow - Russian tycoon Mikhail Khodorkovsky has pulled funding for an investigative journalism project, saying it made mistakes organising a trip to Central African Republic where three of its reporters were killed investigating Russian mercenaries.

The three reporters, working for the TsUR online news outlet, travelled to CAR to investigate the activities of clandestine Russian private military contractors known as the Wagner Group when they were ambushed and killed on July 30.

Khodorkovsky, who has vowed to find those responsible, said the choice of local assistant for the reporters had been a "significant mistake" and that responsibility for that lay in part with TsUR's producers.

Khodorkovsky said he had received a letter of resignation from Andrei Konyakhin, TsUR's chief editor.

"Even partial responsibility is too much in a situation like this. I therefore note the resignation letter of TsUR's chief editor Andrei Konyakhin and stop my support of the (TsUR) project as an investor," he wrote on a social media post.