BOGOTA (REUTERS) - Fifteen policemen were killed on Tuesday when a helicopter fell to the ground and burst into flames in a wooded region of northwestern Colombia, the National Police said.

Police said the US-made UH-60 Black Hawk apparently suffered a mechanical failure while taking part in a counter-narcotics operation in the department of Antioquia some 450km north-east of the capital of Bogota.

"As a result of this incident, 15 policemen were killed and two others wounded," the police said in a statement.

The crash comes four days after 11 soldiers were killed when a Spanish-made CASA C-235 suffered motor failure and crashed in the north-east of the country.

The policemen killed on Tuesday were taking part in a crackdown on a criminal gang known as Clan Usuga, made up of former right-wing paramilitaries.

The head of group, Dario Antonio Usuga, alias Otoniel, leads 2,000 men.

The United States is offering a reward of up to US$5 million (S$6.9 million) for information leading to his capture.

Colombia's security forces have dozens of Black Hawk helicopters that are used in the government's offensive against leftist guerillas, criminal gangs and drug traffickers.