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BOGOTA (Reuters) - Former Marxist FARC rebels who have chosen to join drug trafficking gangs instead of demobilizing will face the full power of Colombia’s military, President Juan Manuel Santos said on Thursday, amid worries gangs will stymie security gains.

More than 11,000 fighters and collaborators from the Revolutionary Armed Forces of Colombia (FARC) handed over their weapons this year as part of a peace accord with the government to end more than five decades of war. The group has kept its initials in its reincarnation as a political party.

But the country’s ombudsman says some 800 former guerrillas did not demobilize, a figure in keeping with estimates of security sources and think tanks who put the number of dissident ex-FARC members as ranging between 700 and 1,000.

FARC leaders have renounced the dissidents and emphasized that the group will move forward as a peaceful political party.

“We’re going to throw everything at these dissidents,” Santos told journalists. “There will be no hesitation.”

Santos said the number of dissidents is below the 15 percent of fighters that he said usually refuse to demobilize when rebel groups lay down their arms after peace deals.

Human rights groups and analysts have expressed worries that a lack of state presence in territory formerly occupied by the FARC is allowing the smaller National Liberation Army (ELN) guerrilla group and criminal gangs to battle for control of lucrative coca crops and illegal mining sites.

Amnesty International said in a report on Thursday that despite a reduction in civilian deaths, the conflict rages on in several parts of the country because of the presence of the gangs and the ELN.