Bogota - The nongovernmental organization Human Rights Watch (HRW) said in its annual report Thursday that the government of Colombian President Alvaro Uribe is blocking the probes of politicians with ties to extreme-right paramilitaries.

The 140-page report, under the headline "Breaking the Grip? Obstacles to Justice for Paramilitary Mafias in Colombia," evaluated progress made and criticized "the influence" of the paramilitaries.

"Colombia's justice institutions have made enormous progress in investigating paramilitaries and their powerful friends," said Jose Miguel Vivanco, Americas director at Human Rights Watch. "But the Uribe administration keeps taking steps that could sabotage these investigations."

The report is based on interviews with prosecutors and investigators, case files, witness testimonies, and other material collected over the course of more than one year.

The South American country's Supreme Court of Justice has made progress on several cases against legislators with alleged ties to the paramilitaries, and the public prosecutor's office has done likewise.

The report claims that the Colombian government has adopted measures aimed at curbing such progress, including public personal attacks on the Supreme Court and its members.

The extradition of high-ranking paramilitaries to the United States just as they were starting to provide Colombian courts with information about their ties to politicians, officials and businessmen in the South American country made it particularly difficult to bring out the truth, HRW said.

"The burden is now on the Uribe administration and Colombia's institutions of justice to ensure that paramilitaries, as well as their accomplices, are held accountable for their crimes," Vivanco said.

Paramilitary organizations were set up in the 1980s, initially as a response to the threat from leftist rebels. Both warring factions are intertwined with the country's illegal drug trade, and have perpetrated numerous crimes against humanity in Colombia, including massacres of civilians.

Under the government of Uribe, over 31,000 members of the paramilitaries demobilized in a peace process with the authorities. However, the Organization of American States (OAS) and others have denounced the emergence of new extreme-right gangs, most of them working in the service of drug traffickers. (dpa)