The army said five soldiers were injured in the attack, adding that it launched the assault on FARC-controlled territory in San Antonio de Getucha, in Caqueta province.

"We launched an operation deep in (FARC's) southern block with a goal of protecting our civilian population," the army said in a statement.

It added that intelligence sources indicated the FARC suffered an "undetermined number of dead and injured" in the fighting.

The latest fighting came just hours before two captive police officers were to be released by the FARC, which has been holding them since last month.

The two officers, Camilo Yate and Victor Alfonso Gonzalez, whom the leftist rebels deem to be prisoners of war, were to be released in southwestern Colombia on Thursday to the International Committee of the Red Cross and the NGO Colombians for Peace.

"We are going to get freedom, we hope, for those two police officers," an ICRC representative, Maryse Limoner, told reporters on Wednesday.

To facilitate their transfer, a military spokesman told AFP that the army would lay down its arms from Wednesday at 6 pm (2300 GMT) to Friday at 6 am (1100 GMT) within the boundaries of the southwestern Colombian states of Valle del Cauca and Cauca.

Earlier this week, the government and the leftist rebels had reported progress on the key issue of land redistribution in their peace talks to end Latin America's oldest insurgency.

But that reported progress comes amid renewed battles between the two sides, after rebels ended a self-imposed moratorium on fighting last month.

Since the Marxist guerrillas lifted their unilateral ceasefire on January 20, they have increased attacks on civilian and military targets, taken hostages and blown up oil and energy infrastructure in a bid to force the government to suspend hostilities.

On Tuesday, suspected FARC guerrillas killed a policeman and a boy and wounded 27 other people, many of them children, in a grenade and gunfire attack in the southern province of Guaviare.