Human Rights Watch accused some of Colombia's top generals Wednesday of links to the "generalized and systematic" execution of civilians, who were then presented as felled FARC guerrillas.

The Colombian military has been under fire for years over the so-called "false positives" scandal, in which army units are accused of killing hundreds of civilians, mostly poor young men, from 2002 to 2008 and reporting them as rebels or drug traffickers killed in combat.

The United States announced Tuesday it had indicted 17 alleged leaders and associates of Colombia's powerful Clan Usuga drug gang, who would all risk life in prison if ever convicted.

They are charged with criminal enterprise, international cocaine trafficking conspiracy and firearms charges in New York and Miami.

Colombia's FARC rebels killed four soldiers and wounded six others in an attack in the northeast of the country on Monday, officials said, as the Marxist group steps up attacks amid unraveling peace talks.

The insurgents attacked soldiers guarding a pipeline in the Norte de Santander district which borders Venezuela.

Experts were battling Wednesday to prevent environmental damage after suspected FARC rebels blew up a stretch of Colombia's second-biggest oil pipeline, authorities said.

Separately, also between midday and late Tuesday, the Marxist guerrillas attacked an army patrol in another part of the country, killing four troops and injuring four others.

Colombian troops have killed the commander of a FARC guerrilla unit and another rebel in an operation near the Venezuelan border, the army said Tuesday.

Elias Tabaco, the head of the FARC's Front 28, and another guerrilla fighter were killed in a "crushing blow" on Monday in a rural region of the eastern department of Arauca, the army said in a statement.

A National Liberation Army (ELN) front leader, also wanted in the 1999 hijacking of an Avianca passenger jet, has been killed in northern Colombia, authorities said Sunday.

"The rebel known as Marquitos, leader of the ELN's Dario Martinez front and a member of its national leadership, has been killed. Congratulations, armed forces," President Juan Manuel Santos said in a message on Twitter, posted while traveling in Rome.

Colombia's FARC rebels killed three police officers Thursday and left nearly half a million people without electricity in two separate attacks, authorities said, in the latest blow to peace talks.

Police said the leftist guerrillas attacked officers on patrol with explosives and gunfire in the southwestern department of Cauca, killing three of them.

FARC rebels blew up a water plant in southwestern Colombia, military officials said Saturday, in the latest alleged attack by the guerrilla movement on the nation's infrastructure.

Fighters with the Revolutionary Armed Forces of Colombia "detonated a high power explosive device" that destroyed the facility in the town of Algeciras, disrupting service to some 13,000 people, a military statement said.

Unknown assailants have abducted the daughter of the director of Colombia's National Protection Unit (UNP), the force charged with guarding people at risk of kidnapping or assassination, officials said Friday.

Eleven-year-old Daniela Mora, the daughter of UNP chief Diego Mora, was abducted Thursday as she left school in Cucuta, a city on the Venezuelan border, authorities said.

Colombian President Juan Manuel Santos said Thursday he welcomes international pressure to accelerate peace talks with the FARC guerrillas, which has mounted in recent weeks as fighting has intensified.

The international community has voiced alarm over Santos's decision in April to resume air strikes on the Revolutionary Armed Forces of Colombia (FARC), a move that prompted the rebels to scrap a unilateral ceasefire they had declared in December.