The leader of one of Colombia's major political parties has been arrested on suspicion of having ties to right-wing paramilitaries.

Carlos Garcia, a senator and head of the National Unity party, which holds the most seats in the senate, was arrested in the city of Santa Marta, the chief prosecutor's office said on Friday.

Garcia is the 31st politician to be arrested over links between paramilitaries and politicians.

Thirty other members of congress, most of them from parties that support Alvaro Uribe, Colombia's president, are under investigation over links to right-wing armed groups formed in the 1980s.

The paramilitaries have been condemned by human rights groups for the killings of trade unionists and political activists and their involvement in the drug trade.

In May, Uribe extradited 14 senior paramilitary leaders to stand trial in the United States on drug trafficking charges.

"The accusation against the senator is that he used paramilitaries to help win elections and consolidate power in his home province of Tolima," a spokesman for Colombia's attorney general's office told the Reuters news agency.

Uribe re-election

Garcia is the second senior member of a party closely tied to Uribe to be arrested in the so-called parapolitics scandal.

In April, authorities arrested Mario Uribe, a former senator, second cousin and confidante of the president, over his alleged links to paramilitary groups.

Garcia had been promoting efforts to allow Uribe to run for a third term in 2010.

Uribe, the United States' closest ally in Latin America, is leaving open the option of running again in 2010, and polls suggest he will win with ease.

But Colombia's scandal-hit congress will first need to approve a referendum vote on whether to amend the constitution to allow him to seek an unprecedented third term.

The law has already been changed once to allow his 2006 re-election.