The World Health Organization is warning that malaria could become resistant to new drugs unless they are used in combination with a second medicine.

Dr. Pascal Ringwald, a medical officer with the WHO, says it is crucial that the drugs be used correctly.

He says so far, the U.N. health agency has not discovered any resistance, but that it is monitoring the situation closely.

New malaria-fighting drugs, derived from a plant known as Artemisia, have been developed in response to other anti-malaria medicines becoming ineffective as resistance developed.

The WHO says the new Artemisian-based drugs must be used together with older malaria medication, such as mefloquine.

The agency estimates the mosquito-borne disease kills more than one million people every year, most of them young children in Africa.

Some information for this report provided by AFP.