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, AFP quoted the police as saying.

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, AFP quoted the police as saying.

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.

The attack came a month after 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.