Four Angolan traditional leaders petitioned a court to re-open investigations into the "blood diamonds" case of seven former army generals they accuse of crimes against humanity.

Angola had opened a case following the criminal complaint brought by anti-corruption activist and journalist Rafael Marques in November 2011. Investigations begun in March 2012, but the case was closed in June.

"This petition calls for the re-opening of the preliminary investigation," Marques said in a statement.

Author of the 2011 book "Blood Diamonds: Corruption and Torture in Angola," Marques has accused the generals of endorsing torture and killings committed by soldiers as well as by private security forces hired to protect diamond concessions in the northeastern Lundas region.

He has singled out the Cuango Mining Society, a consortium that includes a company called Lumanhe, in which he says the generals have a stake.

The local traditional chiefs in the diamond-rich region of Lunda, which produces over a billion dollars worth of gems annually, are also challenging the testimony given by a defense witness during last year's hearings.

They claim the witness made "false statements on behalf of legitimate traditional leaders," according to the statement.

Among the incriminated generals is the Helder Junior "Kopelipa", who is a Minister of State in President Jose Eduardo dos Santos' government.

According to the Portuguese media, the generals in November lodged a libel and defamation case against Marques. The case was filed in Portugal, where Marques's book was published.