Colombia's battle against cocaine production can be won, the US Secretary of State, Madeleine Albright, at the start of her trip to discuss American involvement in the country's anti-drugs war.

However she said the fight "will clearly take hard work and determination".

Mrs Albright's trip - the highest-level US visit to Colombia for 10 years - is linked to US plans to give the country $1.3bn in aid to help fund new counter-narcotics battalions equipped with dozens of attack helicopters.

The package reflects a shift in US strategy to try to stop the drugs trade at source.

An estimated 80% of the cocaine in the US comes from or through Colombia - and production there has doubled in the last four years.

Guerrilla war

However analysts wonder whether the assistance will be enough to allow the Colombian armed forces to defeat the estimated 22,000 left-wing guerrillas and 5,000 right-wing paramilitaries who control the drug trade.

Mrs Albright's visit came as the head of the Revolutionary Armed Forces of Colombia - the country's largest left-wing rebel group - said he was optimistic about peace talks with the government.

Manuel Marulanda was speaking after meeting government representatives in a rebel safe haven in the south of the country.

Peace negotiations between leftist rebels and government began a year ago, but have been making slow progress.

Both sides have agreed on an agenda, but the rebels have refused to lay down their weapons until a peace settlement is finalised.

Combat paramilitaries

A US official travelling with Mrs Albright told reporters that the Colombian Government had to attack right-wing paramilitary groups if it wanted to "wage a vigorous law-and-order programme".

"By our accounts, the largest single human right violators in Colombia are the paramilitaries, so if we are going to spend efforts dealing with human rights issues, we are going to go right into the face, and the Colombian government is going to go right into the face, of the paramilitaries," the official said.

Mrs Albright's visit began at an official dinner in the city of Cartagena where she was the guest of President Andres Pastrana and the Nobel-prize winning author, Gabriel Garcia Marquez.

She said the US was "very impressed" with President Pastrana's plans to deal with narco-trafficing, the peace process and the economy.

The BBC's Jeremy McDermott in Colombia says Mrs Albright's presence has been greeted by the government with undisguised glee.

Mrs Albright also planned to visit Panama and Mexico this weekend.