The 12-minute grainy tape, with a soundtrack of gunshots and birdsong, shows Marxist rebels from the Revolutionary Armed Forces of Colombia (FARC) as they blow up a mayor’s office and police barracks in an unidentified southern town, rob a bank, then tuck into an après-battle barbecue. Laughter and whoops of victory end the session. “This is a demonstration of ruthlessness and cruelty,” said the interior minister, Armando Estrada. “It’s scary because these people could one day be governing this country.”

The footage, believed to be a training video, shows guerrillas, some as young as 11, in camouflage and toying with their submachine guns as a commander reads off items to bring to the attack: grenades, explosives, mortars, and propane missiles. One lad playfully sticks out his tongue at the camera and then shows off the submachine gun he has strapped on his back like a school satchel.

The guerrillas stage marching drills and twirl their weapons smartly as they march. The number of young boys and girls among the ranks is startling. Afterward, they sit in front of a tattered map, awaiting orders.

The attack was in central Tolima province, the army believes, but there are too few landmarks to verify the exact spot. After the bank is demolished, a rebel grins beside a heap of cash, then five police officers offering to surrender are pinned to the floor, submachine guns at their throats. Their fate is unknown. Town residents help guerrillas set up mortar launchers and plant explosives in the streets.

After the attack, teenage rebels, boys and girls, are shown splashing in an idyllic jungle stream. Then an underage burial squad, most wearing brown FARC T-shirts, shovels corpses into hastily dug graves. Rough estimates put deaths in battles during the past decade at 40,000, many civilians.

A FARC commander contacted by phone in the rebel demilitarized zone in southern Colombia said he could not comment on the tape, which was broadcast on Thursday by the network RCN after being leaked by the attorney general’s office. “We go to bed at 8 o’clock at night and this was aired after that,” said Simon Trinidad.

Colombian authorities have issued 1,300 arrest warrants for the guerrillas, clearly identifying them in the tape of the attack. Crimes cited range from subversion and kidnapping to terrorism and murder.

In spite of pledging not to recruit fighters under 15, and even releasing 60 youngsters last year to widespread publicity, FARC leaders have no shortage of volunteer child soldiers. The power and glamor of the rebels attract many homeless youngsters. The international charity Save the Children says modern automatic hand weapons are so light that children can use them easily. Underage volunteers are welcomed by some rebels and by the paramilitary squadrons newly declared terrorists by the United States.