MANILA -- Twenty people, including five army soldiers, were killed and 111 others wounded on Sunday as two blasts went off inside and near the entrance of a Roman Catholic church on the island of Jolo in the southern Philippine province of Sulu, police said.

"Hopefully the number of those killed in the incident will stop at 20," Police Chief Superintendent Graciano Mijares, Philippine National Police (PNP) director in the Autonomous Region in Muslim Mindanao (ARMM), told Xinhua over phone.

Mijares said earlier that 27 were killed in the incident, which took place at around 8:28 am (0028 GMT) on Sunday.

"As of this time, data (are) being reconciled and victims are being identified. There were double entries in the tally of the incident command post this morning regarding data of killed victims," Mijares said in a report.

Many of the injured were taken to local hospitals in Jolo. At least seven of the critically wounded were helicoptered to Zamboanga City, he said.

PNP chief Director General Oscar Albayalde said the bombs are believed to be an improvised explosive device (IED). He said one IED went off inside the church while the other went off outside, near the entrance of the church. "It went off one minute apart," he said.

Col. Gerry Besana, spokesman of the military's Western Mindanao Command based in Zamboanga City, said one of the IED exploded inside the church while a mass was underway. A couple of minutes later, another IED exploded in front of the church killing the soldiers who swiftly responded to the first blast, he said.

Besana said one of the IEDs was placed inside the utility box of a motorcycle parked outside the church.

No group has claimed responsibility for the attack so far. The military and the police are trying to find out who were behind the blasts.

Philippine Defense Secretary Delfin Lorenzana said the Armed Forces of the Philippines (AFP) immediately secured the explosion area and transported the victims to the nearest medical facilities, including the air evacuation of some victims to Zamboanga City.

"I have directed our troops to heighten their alert level, secure all places of worships and public places at once, and initiate pro-active security measures to thwart hostile plans," Lorenzana said.

"As we convey our sincerest condolences to the families and friends of the victims, and offer our sympathy to the peace-loving people of Sulu who are severely affected by this dastardly act, we assure our people that we will use the full force of the law to bring to justice the perpetrators behind this incident," he added.

Lorenzana urged the public to be more vigilant and to be cooperative with the authorities in reporting any security related concerns.

Jolo is the base for Abu Sayyaf militant group, which has recently become better known for criminal brutality, kidnaping-for-ransom activities, bombings, and beheadings in western Mindanao, particularly in their lair in the island provinces of Basilan and Sulu. The group is smallest but also the most radical of Islamist groups in the Philippines.

Last month the AFP created an Army infantry division that will mainly hunt down the elusive Abu Sayyaf terrorists in Sulu province.

The attack took place while Mindanao is under martial rule..