‍The leader of the leftist National Liberation Army (ELN), Colombia's last remaining active rebel force, has been killed in an operation by security forces, Colombian president Juan Manuel Santos said on Thursday.

 "I congratulate our Public Forces for neutralizing Alvaro Gelves Ortega, alias Jairo, 1st leader of the ELN's Jose Antonio Galan Front," Santos wrote on Twitter.

The operation took place in the south of the country's northern Bolivar department, leaving Ortega's "escort" also dead, according to a tweet from General Jorge Nieto, director of Colombia's National Police.

The authorities did not provide further details regarding the operation. The leftist ELN and the Santos government have been engaged in rocky peace talks since February.

The discussions followed a historic disarmament accord last year between the government and the country's largest rebel force, the Revolutionary Armed Forces of Colombia (FARC).

The president of Colombia is trying to achieve "complete peace" by seeking a deal with the ELN without a ceasefire in place. 

(Source: AFP)