We recognise that our efforts to date have not yet produced the results we had hoped to achieve

The White House

Coca crops in Colombia, the world's largest producer of cocaine and the main supplier of the drug in the US, grew to almost 170,000 hectares last year, according to the US estimates.

The White House said the new figures were a source of concern, despite acknowledging that the inclusion of an area not previously surveyed by satellites was responsible for the increase.

"Nonetheless, the increase in cultivation is troubling. We recognise that our efforts to date have not yet produced the results we had hoped to achieve," a White House statement said.

The Colombian authorities disputed the figures, saying they managed to reduce the area cultivated with coca to just under 145,000 hectares in 2001, which represented an 11% drop compared with the previous year.

Volatile situation

The White House stressed that it remained committed to helping Colombia fight drug-production and trafficking, saying that the new figures underlined the need for sustained US engagement.

Colombia supplies more than 80% of cocaine sold in the US

It said the volatile security environment in Colombia was a major obstacle to implementing effective counter-drug programmes.

Colombia is one of the main recipients of US aid, but under current law it can only be used to tackle drug-traffickers, and not against the left-wing rebels who the Americans consider to be terrorists.

However, the United States Congress has recently approved a proposal which could expand US military involvement in the country.

Colombia is embroiled in a civil war that has lasted nearly 40 years - a conflict in which more than 37,000 people have lost their lives.