Jaime Lozada, whose kidnapped wife is still being held by rebels, was attacked as he drove with his son in Huila state, about 300 kilometers (190 miles) southwest of Bogota.
The assailants triggered an explosive device that stopped Lozada's car then opened fire on the vehicle, police said. Lozada's son, Jaime Felipe, was wounded in the attack.
Police spokesman Alberto Cantillo said everything indicated the attack was the work of the Revolutionary Armed Forces of Colombia, or FARC, but that no one had been detained in the attack.
Lozada's sons, Juan Sebastian and Jaime Felipe, were freed in July 2004 after being held by the FARC for three years at hidden jungle camps in southern Colombia.
The FARC has refused to release Lozada's wife, Gloria Polanco, including her on a long list of "political prisoners" it wants to exchange for jailed rebels. But the government and the rebels have been unable to agree on a deal.
The rebel group kidnaps hundreds of people every year as part of its 40-year-old struggle to topple the government.
Lozada, also a former governor of Huila state, acknowledged that he had paid the FARC for his sons' release and said he had received threats from the FARC recently because he still owed them money.
Lozada said he felt humiliated for giving in to the rebels who dragged away his sons and wife from their luxury apartment in Neiva, the Huila state capital, but that he couldn't let them "slowly die in the jungle."
The abduction sent fear through urban Colombians and brought a conflict mainly fought in the countryside to their doorstep. Lozada denounced the government for failing to ensure his family's safety.
After their release, the brothers said they would dedicate their lives' to securing their mother's freedom.
Saturday's attack came a day after suspected FARC fighters gunned down four police officers on foot patrol in a remote town in Huila state before fleeing. Officials offered a US$20,000 (Ђ17,100) reward for information leading to the capture of those responsible.
Congressman Luis Jairo Ibarra said the mounting violence in Huila had made it too dangerous to campaign there for next March's legislative elections. "The political campaign in Huila state has been suspended until the necessary (security) guarantees are in place," Ibarra, who is seeking re-election, told Caracol radio Saturday.
But Huila Gov. Rodrigo Villalba urged candidates not to give in. "It's understandable that they feel intimidated, but what needs to be done is to come up with adequate protection," he said, AP reports. P.T.
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