By Hugh Bronstein

BOGOTA, Dec 12 (Reuters) - Colombian paramilitaries have been weakened but not destroyed despite government assertions to the contrary, the Organization of American States said on Wednesday.

The announcement could further complicate the country's effort at clinching a U.S. trade deal. Democrats in the U.S. Congress say Colombia has not done enough to stop rights abuses by the right-wing militias.

President Alvaro Uribe says his government has dismantled the cocaine-funded "paras" formed in the 1980s by rich Colombians to fight leftist rebels, but OAS representative Sergio Caramagna said the groups still exist.

More than 30,000 former "paras" have turned in their guns over the last four years under a peace deal offering reduced prison terms for crimes including massacre and drug smuggling.

"The demobilization and disarmament has clearly weakened paramilitarism," Caramagna, who monitors Colombia's peace process for the OAS, told reporters. "But we do not think it has ended."

He said that some paramilitaries were rearming and that a man on a motorcycle rode up to OAS headquarters in a poor neighborhood in the city of Medellin last month and threatened to kill the head of the office if she did not get out of town.

"For the first time in four years an official of the OAS mission was threatened in Medellin," Caramagna said.

Police say the threat may have come from the Norte del Valle drug cartel based near the city of Cali or paramilitary thugs who rose in the place of late cocaine king Pablo Escobar. He was based in Medellin before being gunned down in 1993.

One-time paramilitaries and new drug gangs are vying for control of parts of the northern industrial city known in the 1980s as home to the country's most vicious cocaine cartel.

Despite progress against the paramilitaries, Colombia has not reached terms for starting peace talks with Marxist rebels who have been fighting the state since the 1960s and still control wide rural areas in the south of the country.

This Andean country is the world's biggest cocaine exporter, with production running at over 600 tonnes per year, according to the United Nations. (Reporting by Hugh Bronstein; Editing by Xavier Briand)

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