A Chinese pharmaceutical firm plans to recall thousands of anti-malarial drugs supplied to Kenya after discovering a counterfeit syndicate.

The vice-president of Holley-Cotec Pharmaceuticals said 20,000 doses of Duo-cotecxin will be removed from sale.

He told the BBC an analysis of the counterfeit product showed it had very low active ingredients and patients taking it would not be cured.

An estimated 35,000 people die of malaria in Kenya each year.

Duo-cotecxin is one of the artemisinin-based combination therapy drugs highly recommended by World Health Organization to treat malaria and is widely supplied in government and private hospitals in Kenya.

A full dose of Duo-cotecxin costs about $5 in Kenya, the counterfeited drug is being sold for less than $1.

New technology

The Ministry of Health has been spearheading a campaign to crack down on counterfeit drugs that are readily available in the Kenyan market.

Dr Willy Akwale, who heads the government anti-malaria control unit, said this is the first case of a counterfeit supply of artemisinin combination therapy drugs.

"There have been many counterfeits on the sulphur-based anti-malaria drugs before, forcing us to have difficulties in countering the disease," Dr Akwale told the BBC's Focus on Africa programme.

Eric Law, Holley-Cotec Pharmaceuticals' vice-president, said they are yet to locate the source of the counterfeits, but there is strong evidence linking the supplies to Asia.

"We are now going to introduce a new technology to tamper-proof the doses that will be supplied to replace the withdrawn drugs," Mr Law told the BBC News Website.

Health officials warn of a global health catastrophe if a growing trade in fake anti-malarial drugs leads to widespread resistance.

Sophisticated trans-national gangs are thought to be behind the counterfeit drugs, a fast-growing multibillion dollar business.

Meanwhile, the Kenyan government said on Thursday that there has been a dramatic rise in the number of children sleeping under insecticide treated mosquito nets.

It said that a two-year campaign to provide nets at subsidised prices has resulted in more than two-thirds of under five-year-olds sleeping under them.