Colombian authorities have arrested a woman who is suspected of arranging the murder of four boys who were shot to death execution-style in their home, the local prosecutor's office said.

In a case that has shocked the country, the four siblings -- ages four to 17 -- were each killed with a single bullet to the head in the town of Florencia, 370 kilometers (230 miles) south of Bogota.

Leftist guerrillas detonated an explosive charge under a military vehicle, killing three soldiers in northern Colombia, the military said.

Two others were injured in the attack Sunday in Norte de Santander, which borders Venezuela, but they were evacuated and were "out of danger," the army said in a statement.

Venezuelan President Nicolas Maduro said Thursday that a coup being plotted by military aviation officials had been dismantled and those involved detained.

Like his predecessor Hugo Chavez, Maduro frequently announces supposed coup attempts and blames right-wing forces, as well as the United States and Colombia. 

Colombia's leftist FARC guerrillas pledged Thursday to stop recruiting children under 17 years old, increasing the age at which it inducts youths into its ranks from 15 to 17.

"The FARC ... has decided from now on not to incorporate minors under 17 years old into the ranks of the guerrillas, and expresses the wish to soon reach a peace accord with social justice," the rebels' chief peace negotiator in ongoing talks with the government, Ivan Marquez, told journalists.

Colombia's leftist National Liberation Army (ELN) rebels on Wednesday set free a Dutch hostage they had held since January, the International Red Cross said.

The International Committee of the Red Cross and Roman Catholic church mediated in the release of the hostage, whose identity was not released, the ICRC said in a statement on the release in Norte de Santander, in the northeast.

Colombia's ELN fighters, currently in exploratory peace talks with the government, has claimed responsibility for abducting a mayor, saying he was corrupt.

The mayor of Alto Baudo town, in Choco province on the Pacific coast, was kidnapped on December 16 as he traveled on a river in the impoverished region.

Armed men shot dead four siblings aged between seven and 17 in their Colombian home, police said Thursday, with the president lamenting they had been "slaughtered."

All four suffered fatal bullet wounds to the head but a fifth child survived Wednesday night's raid in a rural area of the department of Caqueta, in the southwest, said police, who have launched a manhunt to track down those responsible.

Colombia's former president Alvaro Uribe denied Monday that his onetime intelligence chief had done anything illegal after she was flown home to face charges of spying on his political opponents.

Maria del Pilar Hurtado, the former intelligence chief, was arrested Saturday after surrendering in Panama, where she had lived for more than four years under political asylum.

Leftist FARC guerrillas resumed peace talks with the Colombian government Monday in Cuba, after a year-end break.

The Bogota government and the Revolutionary Armed Forces of Colombia have been negotiating for more than two years in Havana to bring an end to the 50-year insurgency, but key issues remain unresolved, including disarmament and how any agreement should be ratified.

Colombia's former spy chief Maria del Pilar Hurtado was taken into custody Saturday after her forced return from Panama to face charges for illegal wiretapping and other crimes.

"She has been at the headquarters of the prosecutor's office since 5 a.m.," a Colombian government source told Agence France-Presse.