BOGOTA (Reuters) - Colombia’s dissident FARC rebels freed a member of a United Nations team it had taken hostage while he was working on a project to substitute illegal crops with legal ones, the government said on Wednesday.

The Colombian United Nations contractor was seized on May 3 by gunmen close to Miraflores in southern Guaviare province, where coca cultivation has long formed a key part of Colombia’s cocaine production. He was stopped by armed men in a convoy of vehicles.

“The U.N. contractor kidnapped by organized crime in Guaviare has informed his superiors that he has been freed by his captors,” the defense ministry said via its Twitter account.

The rebels, about 300 or so former FARC fighters who rejected a peace accord with the government late last year, want to take over coca cultivation and cocaine trafficking that was abandoned when the Revolutionary Armed Forces of Colombia (FARC) agreed to lay down their weapons.

The government is seeking to substitute coca - the raw material for cocaine - with legal crops such as coffee, fruits and cacao.

The kidnapping came at the same time representatives of the U.N. Security Council were in Colombia to discuss the peace accord signed with the Marxist FARC to end more than five decades of conflict in the Andean country.

While as many as 7,000 fighters agreed to the pact and have turned in most of their weapons to the United Nations, the dissidents refused. They have formed a new criminal gang and now engage in the same lucrative drug trafficking that the FARC had pursued for years, the military has said.

The FARC’s leadership expelled them.

Opposition politicians, including former President Alvaro Uribe, are angry the peace accord allows former FARC fighters to avoid prison time and participate in national politics. Many Colombians say the government has not done enough to prevent other criminal groups and FARC dissidents from filling the void and taking over the drug business.