Colombian union officials said that early on Wednesday morning unknown attackers firebombed their headquarters in the southeastern city of Cali.

The Sintraemcali union, representing employees of municipal-owned enterprises, condemned the attacks on their offices around 2:25 a.m., when according to testimony of the night watchman, four individuals began throwing "incendiary bombs" at the building.

The doors of the headquarters were knocked in, the front of the building was covered in smoke and the water piping burst, which helped to control the flames, the guard said, adding that two of the attackers fled on a motorcycle and the other two left the scene in a taxi.

Colombian Labor Minister Rafael Pardo condemned the attack and asked the director of the National Police, Gen. Rodolfo Palomino, to investigate the incident and provide protection for union leaders.

The attack came five days after a court ordered Colombian President Juan Manuel Santos and Vice President Angelino Garzon to publicly apologize to Sintraemcali and two other Cali unions.

The court found that Sintraemcali, Sintraunicol and Sintratelefonos were harmed by statements made in July 2007 by officials with the 2002-2010 administration of Alvaro Uribe linking union members to front men and allies of the Revolutionary Armed Forces of Colombia, or FARC, guerrillas.

After those accusations, union officials began receiving death threats from right-wing paramilitaries.

Shortly before the start of the trial in 2012, Uribe's vice president, Francisco Santos, retracted the statements and apologized, while erstwhile presidential adviser Jose Obdulio Gaviria did the same after the ruling last week. EFE