Hundreds of African monkeys are being taken from their natural habitat and sold for scientific experiments, as well to a "secretive" biological laboratory in Iran, London's Sunday Times reported.

In an undercover investigation by the Times, Tanzanian animal trader Nazir Manji said he sells some 4,000 vervet monkeys a year to laboratories all around the world for about $100 each.

The monkeys, although listed under the Convention on International Trade in Endangered Species — or CITES — are likely to undergo sometimes painful experiments ultimately leading to their death, the paper reported.

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Manji, who has been exporting monkeys from Tanzania for 22 years, said Iran's Razi Vaccine and Serum Research Institute bought 215 vervet monkeys from him this year.

The biological research institute, which has headquarters near Tehran, has been accused in the past by an Iranian opposition group of conducting biological weapons testing, it is reported, further fueling suspicions that the monkeys are being used for nefarious purposes.

Tanzanian animal dealer Filbert Rubibira was asked last year to prepare a sale for the Chinese military for "scientific purposes."

He told an undercover Times reporter that his company sells animals to any willing buyer, regardless of the fate of the monkeys.

"If it's for scientific, if it's for the zoo, if the plane is accepted for transport they don't care about that ... The purpose is not a problem," Rubibira told the paper.

Animal-rights groups are reportedly calling on CITES authorities to investigate.

• Click here to read the full report in London's Sunday Times.