The boy died after three months in captivity, having been taken from his school in the Amazon by guerrillas and other criminal groups fighting Colombia's leftist government.

He was among seven children killed in the bombing on a guerrilla outpost in the jungle department of Guaviare that claimed 20 lives in all.

All the minors had been kidnapped by members of a group that calls itself the Central General Staff (EMC), made up of dissidents who continued fighting after the FARC guerrilla army disarmed under a 2016 peace agreement.

"They were just children who were barely learning to live. Where they should have been was studying in school, playing," lamented the boy's sister, herself barely 18 and unnamed for fear of reprisals.

She blames the guerrillas who took him, but also the government.

"This should never have happened," she told AFP at a morgue in the central city of Villavicencio where the bodies were taken for families to claim -- hundreds of kilometers from Guaviare.

"President Gustavo Petro should never have done this. Knowing there were minors, he nevertheless authorized" the bombing, the young woman added.

- 'Deep concern' -

Since August, military strikes targeting rebel fighters have claimed the lives of 15 abducted children, Colombian officials said Monday.

The UN Human Rights Office in Colombia has expressed "deep concern" over military killings of minors who are kidnapped by rebels, usually to be trained as fighters themselves.

Prosecutors say more than 1,100 children were abducted by armed groups between 2019 and 2023.

From 1996 to 2016, the number was as high as 23,800.

With six months to go to presidential elections, Colombia's first-ever leftist government has come under opposition pressure over a perceived leniency towards guerrilla and drug trafficking groups that in the 1980s and '90s terrorized the South American country.

Also under fire from US counterpart Donald Trump, Petro has abandoned his stated commitment to "total peace" through negotiation, launching an offensive on cocaine-producing enclaves run by a variety of armed groups.

Petro himself has said the Guaviare bombing that killed the 16-year-old was to thwart an imminent attack by EMC forces led by Ivan Mordisco, the country's most wanted guerrilla leader.

- 'Not to blame' -

His sister said the teenager had attending a rural school in Guaviare when he was taken by guerillas.

His father went to look for him, but gave up "out of fear," she recalled

"The only thing they told him was to stop looking," she added.

Petro had refused to halt the bombings despite a request from the office of Colombia's human rights ombudsman.

The office says the forced recruitment of minors increased by 36 percent between 2023 and 2024, calling it a "complete failure" of policy.

Between January and October this year, the entity received 162 complaints -- half of them concerning Indigenous children from poor, rural areas taken against their will.

Mordisco's group was responsible for 40 percent of cases, according to official data.

The 18-year-old clung to the arm of a relative as she waited for the body of her brother, "who meant everything to me."

The children killed, she insisted, "are not to blame for anything."