Police in the southern Philippines city of Zamboanga city are investigating the explosion of two small bombs, one of which exploded outside a Catholic cathedral early Sunday morning, Reuters reports.  Muslim insurgents are suspected in the attack.

The first bomb’s blast shattered the windows of the cathedral and damaged two vehicles parked near the building.  The explosion created a half-inch deep crater on the blast site. 

Three men reportedly were seen riding a motorcycle near the location and leaving a bag in the area minutes before the explosion.

The Philippine military on Sunday said the bomb could have been intended to disrupt the 5 a.m. Mass but went off prematurely. 

Another bomb exploded near a coffee shop about half a mile away from the cathedral.

No one was injured in either blast.

"Whoever did this apparently did not want to cause real damage, just sow fear," Colonel Darwin Guerra, a commander of a local task force, told local radio.

Archbishop of Zamboanga Romulo Valles denounced the attack. 

“We are greatly saddened by these incidents. It is clearly an act of darkness. We should stand united,” the archbishop said.

According to Reuters, the city’s police chief said authorities were considering the possibility that militants trained by regional terror group Jemaah Islamiah were responsible for the attacks.

“We found traces of a mortar round and a mobile phone at the blast side," said Superintendent Jonathan Perez, saying the Saturday attacks were the first time that style of bomb had been used in the city.

The Philippines is fighting Muslim insurgencies in its southern islands.  Since 2002, Washington has been training and equipping its former colony to hunt down terrorists.  Dozens of U.S. Special Forces members are based in Zamboanga City.