Evo Morales, the Bolivian leader, ate a coca leaf in front of delegates at the UN summit on drugs yesterday, to underline his demand that the raw ingredient of cocaine should be allowed for medicinal and other uses.

President Morales, a former peasant coca farmer, brandished the leaf during an impassioned speech, saying: "This is coca leaf, this is not cocaine, this is part and parcel of a culture." He told ministers that the ban on coca was a "major historical mistake".

He added: "It has no harmful impact, no harmful impact at all in its natural state. It causes no mental disturbances, it does not make people run mad, as some would have us believe, and it does not cause addiction."

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Coca is commonly used in Bolivia and Peru to stave off hunger and altitude sickness, as well as being used in cooking.

Mr Morales, who also said that he was dedicated to tackling the trade in illicit drugs, including cocaine, said that he hoped US President Barack Obama would support his campaign.

"The new US President has similarities to me," he said.

"Before, nobody believed that an Indian could be president and nobody thought that a black man could be president of the United States."