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 U.S.-made UH-60 Black Hawk apparently suffered a mechanical failure while taking part in a counter-narcotics operation in the department of Antioquia some 450 km northeast (280 miles) 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 northeast 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 $5 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 guerrillas, criminal gangs and drug traffickers.