Al-Qaeda-linked Islamist Abu Sayyaf rebels beheaded seven workers they abducted earlier this week on a southern Philippine island, the military said on Friday.
The decapitated heads of the seven workers were delivered to two military outposts in Parang town on Jolo island, 1,000 km south of Manila, on Thursday.
Brigadier General Ruben Rafael, head of an anti-terrorism task force, said the Abu Sayyaf rebels blocked two vehicles and forced the drivers to deliver the heads, which were placed in sacks.
"This is in retaliation for the recent killing of their commanders," Rafael said. "This is a terrorist act that should be condemned by all."
Top Abu Sayyaf leaders have been killed in a months-long military offensive in Jolo, including Abu Sayyaf chieftain Khadaffi Janjalani who died in a firefight in September 2006.
Janjalani's body was found in December 2006 and his death confirmed in January.
The seven victims were abducted on Tuesday by rebels led by commander Albader Parad. They were working on a government road project in Parang.
Police said the guerrillas had demanded five million pesos ($105,000) in ransom.
The Abu Sayyaf is the smallest but most violent Muslim rebel group in the southern Philippines. It has been blamed for some of the worst terrorist attacks in the country.