The BBC's South American correspondent Richard Collings reports from Bogota (1'23")

Ties have been strained for the past four years, with the outgoing President, Ernesto Samper, accused of receiving money from drug-traffickers.

The US State Department spokesman, James Rubin, offered warm congratulations to the Conservative Mr Pastrana.

He said the United States was seeking to arrange a meeting with him as soon as he takes office in August, to discuss what he termed as co-operation and assistance.

Request to US for help with war on drugs

The BBC's Richard Collings: "Talks with guerrilla groups could take place next week." (1'35")

For his part Mr Pastrana, said he wanted the United States to play a role in peace talks with Colombia's left-wing guerrillas who derived much of their financial support from the drugs barons.

He said he had received assurances from the rebels that they will eradicate drug crops in areas under their control and pledged to meet with their leaders maybe as early as next week.

Correspondents say Mr Pastrana faces a difficult term.

Under President Samper, unemployment doubled and the country's economic growth almost halved.

These factors, combined with scandals, are thought to have driven many voters to switch from the Liberal party, which has governed for 12 years, to Mr Pastrana's Conservatives.

Troubled economy

Over the past few weeks Colombia's currency, the peso, has been hit by a wave of speculative attacks.

Its sharp fall in value against the US dollar has led to massive Central Bank intervention. Local stock markets have also fallen to 17-month lows.

Andres Pastrana:"I aim to be the president of peace and social justice" (in Spanish)

Mr Pastrana has promised swift austerity measures to deal with the growing economic crisis and promised to be "the poor man's president."

In a speech immediately after his victory, he said: "I receive the country with its finances in a disastrous state. One of the most urgent priorities of my government, therefore, will be to restore confidence among economic agents and put the budget house in order.

"We're going to propose to the country, Congress and the international financial community a serious and vigorous fiscal adjustment programme which we will carry out promptly."

Long Liberal rule ends

Serpa: dogged by party's alleged drugs links

Mr Pastrana defeated Horacio Serpa, the candidate of the Liberal Party of the outgoing President, Ernesto Samper, by five points.

The Liberals were harmed by allegations that they received millions of dollars from drugs barons but the party retains its hold on Congress.

The BBC's Richard Collings: "Pastrana has spent a decade trying to win." (1'10")