Scots actor Alan Cumming has called for a chimpanzee he describes as his "old friend" to be released from captivity.

Tonka, who starred alongside the award-winning British actor in the 1997 movie Buddy, is living out his final days in a cage at the Missouri Primate Foundation, in Festus.

The owner of the animal centre, Connie Braun Casey, has repeatedly been cited by the US government for violating federal animal-welfare regulations.

It is claimed by animal activists that the chimpanzees at the centre live in small and filthy cages.

The majority of its apes are discarded acting animals and pets.

The Missouri Primate Foundation have denied all of PETA's claims and are currently suing the group - they brand a 'militant, activist, animal rights group' - for defamation.

Last week, Cumming wrote to Casey asking her to release Tonka from her facility.

The 52-year-old wrote in his letter that he had developed "a very close camaraderie" with the chimp during the months they filmed for Buddy.

He wrote: "It was a special friendship - one I'll always treasure.

"I hoped to see Tonka the following year at the film's premiere but was told that he was no longer manageable and had been "retired to Palm Springs.

"Over the past 20 years, I imagined him living out his post-Hollywood years on a sprawling sanctuary," he continued.

"I just learned, though, that Tonka didn't end up at a sanctuary in Palm Springs but inside a cage in Festus.

"He isn't able to have complex social relationships with other chimpanzees and doesn't have meaningful outdoor access to run, climb, or play."

"As an old friend of Tonka's, I respectfully ask that you allow him and the chimpanzees at MPF to be sent to accredited sanctuaries where they can enjoy some semblance of the life that nature intended for them."

PETA sent notice of their intent to sue under the Endangered Species Act (ESA) last year.

The notice said that the foundation had "taken" chimps illegally and that they were denied complex and sanitary environments, while at least one chimp was kept in isolation.

However, the Primate Foundation hit back with their own lawsuit in December.

They claimed PETA's allegations were false, and were seeking to bar the group from filing the animal welfare suit while also alleging defamation.

The Missouri Primate Foundation, which was set up by Casey and her ex-husband Mike, was criticised by the animal welfare group.

The group alleged that the facility was little more than the "filthy" converted home of Casey.

They say that chimps are kept in small cages, some within a converted bedroom with no direct access to the outdoors and others in the basement and another prison-like addition to the home.

Travis, the chimpanzee who famously ripped off the face and hands of a Connecticut woman in 2009, had been born at the Missouri Primate Foundation and sold by Casey as a "pet".