The Rwandan official accused of masterminding the savage murder of Dian Fossey, the US zoologist made famous by the film Gorillas in the Mist, has been arrested in Belgium and is likely to be interrogated by the FBI, it emerged yesterday.

Protais Zigiranyirazo is also wanted for allegedly playing a key role in the planning of the 1994 Rwandan genocide in which 800,000 Tutsis and moderate Hutus were murdered. He will be extradited to the UN war crimes tribunal in Tanzania within the month.

Mr Zigiranyirazo, known to his countrymen as Monsieur Z, is accused of ordering Fossey 's death in December 1985 because of her campaign against the poachers killing the mountain gorillas she loved.

Fossey burned poachers' houses, led anti-poaching patrols, placed bounties on poachers' heads, killed any of their cattle which strayed into her conservation area, and ordered her students to carry guns. She did everything she could to protect the gorillas.

According to the Rwandan authorities, it was Mr Zigiranyirazo, a local government official, who ordered her murder.

Fossey's mutilated body was found in her cabin at the Karisoke research centre in Rwanda, the isolated park where she had monitored the gorilla population for 18 years. She had been hacked to death with a machete.

Her case received worldwide attention in 1988 when Sigourney Weaver played her in the film Gorillas in the Mist.

The Belgian government has informed the FBI that Mr Zigiranyirazo is in custody and officials say it is likely that the US agency will dispatch investigators to Belgium or Tanzania to question him.

Mr Zigiranyirazo, 63, was first arrested by the Belgian immigration authorities at Brussels airport for travelling on a false passport, which came to light when he claimed asylum inthe country.

A well-known businessman, Mr Zigiranyirazo is the brother-in-law of the former Rwandan president Juvenal Habyarimana, whose death in 1994 sparked the genocide.