A British charity set up to fund conservation parks in the Congo basin knew about allegations that tribal people were being abused by park guards but failed to alert the charities’ watchdog, the Guardian can reveal.

Last week, WWF launched an inquiry into claims that it has funded paramilitary guards accused of torturing, sexually assaulting and murdering people in Africa and Asia. In response to the claims, published by BuzzFeed News, the organisation said it has “stringent policies” to ensure the safeguarding of indigenous peoples’ rights and would take “swift action” should the review uncover any breaches.

The Sangha Tri-National Trust Fund Ltd (FTNS) funds a protected area consisting of three adjoining national parks covering areas of Cameroon, Central African Republic and Congo. The charity, which also funds an anti-poaching brigade, aims to support best practice in wildlife conservation and the “socio-economic well-being of communities”, according to its website.

Abut 14% of FTNS’s €3m (£2.5m) funding to the parks went to “surveillance and anti-poaching operations”, according to its’ 2017 annual report.

The Charity Commission said it would be contacting FTNS to “remind them of our guidance on reporting serious incidents”.

“We will expect the trustees to inform us of the outcome of their investigation,” said the commission, which last week received a serious incident report from WWF UK over abuse allegations.

Charities are required to submit a serious incident report when “a beneficiary or other individual connected with the charities activities has or alleges to have suffered serious harm”.

This requirement was highlighted by the commission last year, following allegations that Oxfam covered up sexual abuse in Haiti.

Simon Counsell, director of Rainforest Foundation UK, called for an investigation. He said: “The Sangha Tri-National Trust has been paying to equip ‘eco-guard’ brigades that have been implicated in serious human rights abuses. The UK Charity Commission needs urgently to investigate whether the charity’s activities have caused harm to local communities.

“The UK and other international donors such as Germany, US, Norway and the EC need to ensure that funding for nature conservation does not harm local people, and safeguards are upheld, including where funding goes through intermediary organisations.”

One of the trust’s directors works for WWF in Germany. A document from the trust’s biggest funder, German state-owned development bank KfW, describes as “credible” testimonies of villagers alleging “abusive searches, beatings and even gunshot wounds” in two parks, including Nouabalé-Ndoki, an FTNS-funded park in the Republic of the Congo. The testimonies were included in a 2017 report from RFUK.

The German bank acknowledged “similar difficulties were encountered in Lobéké, another park funded by FTNS in Cameroon, and called for an independent investigation. KfW described FTNS as an “implementing agency” in a project it funded to organise, equip recruit and train anti-poaching brigades. Survival International published claims of abuse by eco-guards linked to WWF in 2016.

German MP Eva Schreiber said KfW had a “moral responsibility” to investigate abuse claims in the Congo basin and Sangha tri-national area. She described the studies conduced by KfW so far as “ridiculous” and “inadequate”.

“This is not just a problem for WWF, this is also a problem for the German government and KfW,” said Schreiber. “First, they have funded a huge part of the budget of these protected areas. That means these protected areas would probably not exist without them.

“Secondly, they have had information about human rights violations from us and NGOs for years, but have not adequately investigated those allegations.”

She said KfW told MPs it pays for the equipment, training and part of the salary of eco-guards, although weapons and ammunition are explicitly excluded.

KfW has contributed €65m to FTNS so far, and provided 61% of the charity’s funding in 2017. A KfW spokesperson said in a statement that the bank has commissioned two studies in relation to abuse allegations made by RFUK and Survival International.

The statement said: “KfW takes the allegations very seriously and we will continue together with our implementation partners to improve the situation of the population living in and near the protected areas”.

The Berlin-based Centre for Rural Development will now review “conflicts, participation and co-management in protected areas” of Lobéké park in Cameroon. Another would “explore how to better promote human rights in conservation projects in the Congo basin”.

KfW said it had contributed €45m to the endowment fund of the FTNS, for the running costs of protected areas. An additional €20m had been provided for “projects for investments, equipment, promotion of tourism and improvement of the peoples’ livelihoods” that were implemented by the FTNS “in cooperation with the international NGOs and the governmental parks’ administration”.

Théophile Zognou, the executive director of the FTNS, based in Yaounde, Cameroon, said in a statement: “We regularly go down to the three parks as part of our follow-up missions and if there were serious problems, we would have alerted the Charity Commission; and even following last year’s claims of Survival International, we have made checks that have not yet proven accurate. In any case, we are now conducting an investigation and the results will be the subject of a communication.”

Zognou said eco-guards in Lobéké national park were recruited and mainly trained by Cameroon.

“WWF [only] provides technical assistance and has organised human rights training for eco-guards from Lobéké and other parks in Cameroon.”

In a subsequent email, Zognou asked for the statement to be amended to say FTNS had found Survival International’s claims were “not accurate”. He also requested that the word “investigation” be altered to “study.” No evidence was offered to support the requested amendments.