A powerful bomb exploded at the center of the southern Philippines city of Cotabato on Monday, killing six people and wounding more than two dozen others, police said.
The explosive device was placed in a vehicle — either a motorcycle or a van — parked near a hospital and a school during the afternoon rush hour, city police chief Senior Superintendent Rolen Balquin said.
Cotabato photographer Mark Navales, who was on the scene within half an hour of the blast, described seeing a blood-spattered road strewn with charred bodies and smoldering vehicle parts.
"I saw three mangled human remains, one of them burnt," he told AFP.
"I have never before seen (the effects of) such a powerful blast in Cotabato," he added.
The attack came a month after the United States, Australia and Canada warned their citizens against travelling to Cotabato and two other southern cities over fresh threats of terrorism.
Those killed were motorists passing through Sinsuat Street, the main highway in Cotabato that is lined by commercial establishments.
At least 26 others were wounded, including police officers in a vehicle that was passing through the area, he said.
No group immediately claimed responsibility.
Mujiv Hataman, governor of a regional autonomous area whose office is 2,625 feet away from the blast site, said the explosion rattled his windows and shattered a quiet afternoon just before Muslims were to end their Ramadan fast.
"That area has always been a busy street, full of traffic. There are a lot of establishments there and people come and go at all hours," he told AFP by telephone.
"The blast was heard kilometres away. It was powerful," he said.
The late-afternoon explosion damaged at least four vehicles and triggered a fire that engulfed a nearby mortuary and a tyre repair shop, he added.
No group has claimed responsibility for the attack, and Balquin said the motive was still being investigated.
Cotabato is a mixed Muslim-Catholic city on the main southern island of Mindanao, where Muslim insurgents have waged a decades old rebellion that has claimed 150,000 lives.
It was the second bombing to hit Mindanao in 10 days.
A powerful blast at a restaurant packed with doctors and pharmaceutical salesmen left eight people dead on the Mindanao city of Cagayan de Oro on July 26.
The Cotabato explosion also came just shortly after the Bangsamoro Islamic Freedom Fighters, a breakaway rebel faction, warned of intensified attacks against the government targets.
In 2011 the BIFF split from the 12,000-strong Moro Islamic Liberation Front (MILF), which is negotiating peace with the government of President Benigno Aquino.
Three BIFF guerrillas were killed last week near Cotabato in clashes after they fired on an oil tanker and laid two roadside bombs.