Colombian President Juan Manuel Santos said Friday he was willing to negotiate with the United States to allow a jailed FARC leader participate in peace talks -- a long-standing demand of the leftist rebels.

"If it is important to achieve peace, I don't have any problem acting on this," the president said when asked about his stance on FARC leader Simon Trinidad during an interview with Caracol Radio.

Trinidad, 63, whose real name is Juvenal Palmera, was extradited to the United States December 31, 2004 and sentenced to 60 years in prison for the abduction of three US citizens, who were held for four years by the FARC after their capture in Colombia.

When peace talks opened in Cuba in November 2012, Colombian authorities suggested it might be possible to allow Trinidad to participate via teleconference from his cell.

The FARC, however, has demanded Trinidad's outright release, in January appealing to the Red Cross to intervene on humanitarian grounds, alleging he is held in isolation and not provided adequate medical care.

Santos cautioned that he could not ensure the United States, where Trinidad is jailed in a "supermax" prison in Colorado, would allow any level of participation.

"It is possible to envision that we would take steps to see if it is possible," Santos said, without giving details.

"If the United States agrees, this could succeed, but at the moment, nothing has moved forward," said the president, who is up for re-election in a vote two days away.

The vote has been seen as a test of the peace process, with Santos presenting his bid for a second term as the best choice for Colombians to finally secure an end to the half-century-old conflict with the Revolutionary Armed Forces of Colombia (FARC).

His nearest rival, former finance minister Oscar Zuluaga, is a leading opponent of the peace talks, and has vowed to suspend the negotiations and give the guerrillas eight days to stop their "criminal actions against Colombians."

The peace talks seek to end Latin America's longest-running conflict, which has left hundreds of thousands of people dead and displaced more than five million since it erupted in 1964.