Efforts to identify the four corpses found near an air force base on Christmas Eve have been complicated by their badly burned state.

The United Nations' human rights office and children's agency UNICEF have issued a joint call for the South American nation to carry out a "thorough, swift, and impartial investigation."

Here is what we know about the case of the four boys aged between 11 and 15:

- How did the boys vanish? -

Saul Arboleda, Steven Medina and brothers Josue and Ismael Arroyo went out to play football in the western city of Guayaquil on December 8 and never came home.

That night, someone contacted the Arroyo family and put Ismael on the phone, according to his father.

The boy said that soldiers had chased them, fired in the air, and forcibly taken and beaten them, he told local media.

Later, the relatives received two locations via WhatsApp, one of them in the town of Taura, home to a military air base, and the other near a shrimp farm.

An anonymous caller told the family that criminals had taken the boys.

On Tuesday, after the courts determined the case was a "forced disappearance," four bodies were found in a mangrove near the Taura military airport, according to local media.

- What was the military's role? -

An unverified video released by Congress appears to show a group of soldiers putting one of the minors in a vehicle and beating him, while another was seen face down.

Defense Minister Gian Carlo Loffredo said that the soldiers were responding to a request for help due to a robbery.

The four bodies "are destroyed and incinerated" which makes identification difficult, Billy Navarrete, executive director of the Committee for the Defense of Human Rights of Guayaquil, which is supporting the parents, told the press.

The boys' relatives were called on Christmas Day to attend the Guayaquil morgue.

If they cannot identify the remains, officials will carry out DNA tests, which usually take at least a month.

- What have authorities done? -

The public prosecutor's office requested that a time and date be set to draw up charges against the 16 soldiers who participated in the military operation.

On Monday, authorities raided the Taura base and confiscated the phones of the suspects and the vehicles used to transport the minors.

The defense ministry placed the 16 soldiers in military detention.

Loffredo said on Thursday that "nothing the children have done justifies their disappearance."

He described the case as an attempt to make Ecuadorians believe "that soldiers are crazy people who go out in gangs of 16 to roam football fields to kidnap and disappear minors," the minister said.

The disappearance has sparked widespread indignation in Ecuador, where kidnapping, extortion and murders are now commonplace.

President Daniel Noboa has boosted the use of security forces to battle powerful drug gangs in Ecuador and sworn to turn back the tide of violence engulfing the once-peaceful country.

He has indicated that the minors could be declared "national heroes."