Colombian President Alvaro Uribe has publicly apologised for the army's killing of five peasant farmers.
Uribe promised no let-up in the fight against guerrillas
The five, including a baby, were shot dead by army soldiers who say they mistook them for guerrilla fighters.
In a nationally televised address, Mr Uribe said the incident was a tragic episode, but rejected calls to moderate the anti-guerrilla campaign.
Earlier, Mr Uribe met relatives of the victims, and said he was personally taking charge of the investigation.
The deaths are the latest in a series of deadly errors by soldiers.
Last month, the Colombian army killed seven policemen and four civilians by mistake in an ambush, and in February, a student was shot dead by a sentry at a military base.
The Colombian army blamed the latest incident on poor visibility.
The Reyes family was killed on Saturday in the southern province of Narino - a guerrilla stronghold. It is believed that when the civilians saw figures in uniform, they mistakenly thought it was a rebel patrol.
In a nationally televised address to the nation on Monday, Mr Uribe said the "tragic episode fills us with grief, but it cannot slow our drive to bring security back to Colombia".
There are fears Colombia's soldiers are becoming trigger-happy
"Every moment we are spurring our soldiers and police officers, demanding results and insisting on rigorous transparency," he said.
Some Colombian senators have argued that President Uribe's demand for quick results against rebel groups is leading to mistakes.
The army has launched a relentless offensive against Marxist rebels and right-wing paramilitaries, pushing the former deep into their jungle strongholds and the latter to the negotiating table.
However, a side-effect has been the fact that soldiers are now shooting first and asking questions later, says the BBC's Jeremy McDermott in Colombia.