The attack is believed to have been carried out by suspected members of the National Liberation Army (ELN) at a military base in the department of Northern Santander.
President Petro took to social media to express his "total rejection of the attack" against seven soldiers and two non-commissioned officers. He described the attackers as "those who today are decidedly distant from peace and the people.
The president quickly called for a meeting with the government commission taking part in peace talks with the rebels to analyze the incident that could jeopardize the transactions.
"I have summoned the government delegation to the peace talks with the ELN, and the guarantor and accompanying countries for consultation. A peace process must be serious and responsible to the Colombian society," he wrote.
"We reject the violent attack allegedly perpetrated by the ELN in North Santander," said Defense Minister Ivan Velasquez in social media.
The Colombian Armed Forces also condemned the attack, which injured eight other fighters, and said it would continue its military offensive against the guerrillas.