The four Indigenous children who had been missing for more than a month in the Colombian Amazon rainforest after a small plane crash have been found alive, President Gustavo Petro announced Friday.

"A joy for the whole country! The 4 children who were lost 40 days ago in the Colombian jungle were found alive," Petro wrote on Twitter.

His post included a photograph of several adults, some dressed in military fatigues, attending to the children who were sitting on tarps among the dense forest.

"They are weak. Let's let the doctors make their assessment," Petro told the press in Bogota.

Originally from the Uitoto Indigenous group, the children -- aged 13, nine, four and one -- had been wandering alone in the jungle since May 1, when the Cessna 206 in which they were traveling crashed.

The bodies of three adults who had been with them -- their mother, the pilot and a relative -- were all found at the crash site by the army.

A massive search by 160 soldiers and 70 Indigenous people with intimate knowledge of the jungle had been under way ever since for the youngsters, garnering global attention.

The area is home to jaguars, snakes and other predators, as well as armed drug smuggling groups, but ongoing clues -- footprints, a diaper, half-eaten fruit -- led authorities to believe they were on the right track.

Worried that the children would continue wandering and become ever more difficult to locate, the air force dumped 10,000 flyers into the forest with instructions in Spanish and the children's own Indigenous language, telling them to stay put.

The leaflets also included survival tips, and the military dropped food parcels and bottled water.

Rescuers had also been broadcasting a message recorded by the children's grandmother, urging them not to move.

- 'A magical day' -

Huitoto children learn hunting, fishing and gathering and the kids' grandfather, Fidencio Valencia, had told AFP the children are well acquainted with the jungle.

"Today we have had a magical day," Petro told the media upon his return from Cuba, where he signed a six-month truce with Colombia's last active guerrilla group, the ELN.

"Getting closer and attaining peace in the agreement that is moving forward with the ELN... And now I return and the first news is that indeed the Indigenous communities that were in the search and the military forces found the children 40 days later," he said.

"They were alone, they made it on their own. An example of absolute survival that will go down in history," he added.

Petro had announced that the children had been found alive 17 days after they disappeared, but retracted the announcement a day later, saying he had been given false information.

Valencia, the children's grandfather, confirmed to AFP on Friday that the children had been found.

"I need a flight or a helicopter to go and get them urgently," he said.

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