"The bombing was aimed at the narcoterrorists," Colombian air force chief Edgar Lesmez told reporters. "We are evaluating the results of the operation."

Police estimate that coca fields planted in the park help the Revolutionary Armed Forces of Colombia, a 41-year-old rebel army known by its Spanish initials FARC, produce 27 metric tons of cocaine every year.

A FARC mortar attack on Wednesday brought to 12 the number of police killed in the first month of "Operation Green Colombia," which the government says is aimed at removing illicit crops from natural parks, starting with La Macarena, in an effort to restore their biodiversity.

An increasing proportion of Colombia's coca fields are being planted in the parks as growers flee a US-funded crop-dusting campaign. The government decided not to dust in the parks after objections from environmentalists who said spraying herbicide would damage protected ecosystems.

More than 900 shovel-wielding civilian workers, ringed by about 1,500 soldiers and police, are moving through La Macarena, pulling up coca bushes.

Bombing within the park presents its own environmental problems, environmentalists said.

"This is part of a chain of errors that has characterized Colombia's eradication program," Fabio Arjona, director of Colombia's chapter of environmental group Conservation International, told Reuters.

"The fumigations have caused great environmental damage in other areas of the country and bombing La Macarena will be catastrophic for the local ecosystem, which includes endangered species," he said.

Lesmez said the bombing did less damage to the environment than what the FARC's cocaine production operation was doing.