Octavio Guzman, the governor of the region of Cauca, said on social media platform X the device was set off on a bus travelling along the Pan-American Highway in the municipality of Cajibio.
Five children were among the injured, Cauca Health Secretary Carolina Camargo told Noticias Caracol, a TV news program.
"Cauca cannot continue to face this barbarity alone. We are facing a terrorist escalation that demands immediate responses," Guzman said.
"We demand forceful, sustained and effective action from the national government in the face of the grave public order crisis we are experiencing," he added.
General Hugo Lopez, commander of Colombia's Armed Forces, described Saturday's explosion in a press conference as a terrorist act.
He blamed the networks of a man known as Ivan Mordisco - one of Colombia's most wanted figures — and the Jaime Martinez faction.
Both are dissident groups of the now-defunct Revolutionary Armed Forces of Colombia (FARC) that operate in the region and did not adhere to the peace agreement signed with the state in 2016.
Colombian President Gustavo Petro decried the attack on X, citing earlier casualty estimates.
"Those who carried out the attack and killed seven civilians - and wounded 17 others - in Cajibio - many of them Indigenous people - are terrorists, fascists, and drug traffickers," he wrote.
The attack is the latest in a spate of explosives attacks and thwarted attempts to target public infrastructure.
At least 26 criminal incidents have taken place in the past two days in southwest Colombia, which Lopez said has only affected civilians.
No one was injured in the previous assaults, which include a shooting at a police station in the rural area of Jamundi, and an attack on a Civil Aviation radar facility in El Tambo, where authorities took down three explosives-laden drones earlier on Saturday.
On Friday, two vehicles rigged with explosives were detonated near military units in Cali and Palmira, causing material damage.
With AP
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