ISIL claims responsibility for the attacks that killed 20 people and wounded more than 100.
Duterte met top defence, military and police officials inside the Cathedral of Our Lady of Mount Carmel in Jolo, Sulu province, before proceeding to a mass wake for victims of the bombing, according to photos posted by a former senior aide of the president.
Before Duterte’s visit on Monday, Oscar Albayalde, the country’s police chief revealed that the brother of a slain Abu Sayyaf leader is a suspect in the attack on Jolo, an island in Sulu province in the restive south.
He identified the person by his alias, Kamah, brother of Abu Sayyaf leader Surakah Ingog. The suspect, who the police said is a known bomb-maker, was caught on security camera footage near the church shortly before the attack.
Kamah is still at large, the police chief said, adding that about 4kg of explosives were used in the bombing.
LOOK: Suspects in the Jolo bombing as captured by security cameras.
— ABS-CBN News (@ABSCBNNews) January 28, 2019
The attack came six days after a referendum on expanded autonomy for the mainly Muslim region returned an overwhelming “yes” vote amid hopes the plan would bring development, jobs and peace to a region long plagued by poverty and instability.
The first blast went off inside the cathedral and was followed by a second explosion outside the compound, which was detonated as security forces raced to the scene, officials said.
The initial bomb scattered the wooden pews inside the Cathedral of Our Lady of Mount Carmel and blasted window glass panels, witnesses said. The second hurled human remains and debris across a town square fronting the church.
Police said the blasts killed 15 civilians and five soldiers, revising an earlier death of 27. More than 110 were wounded.
“The enemies of the state have boldly challenged the capability of the government to secure the safety of the citizenry in that region,” said Salvador Panelo, Duterte’s spokesperson.
“The armed forces of the Philippines will rise to the challenge and crush these godless criminals.”
The Islamic State of Iraq and the Levant (ISIL, also known as ISIS) claimed responsibility for the attack via its Amaq website.
Police are investigating the claim but suspect it was the work of Abu Sayyaf, a domestic armed group that has pledged allegiance to ISIL and has carried out bombings, kidnappings and beheadings in the strife-torn southern region of Mindanao.
“They want to show force and sow chaos,” Albayalde told DZMM radio, suggesting Abu Sayyaf was the prime suspect.
In a statement, the Philippine army said the explosions were likely caused by improvised explosive devices (IEDs).
Photos on social media showed debris and bodies lying on the busy street outside the cathedral, which has been hit by bombs in the past.
Troops in armoured carriers sealed off the main road leading to the church while vehicles were transporting the dead and wounded to the hospital.
Some casualties were evacuated by air to nearby Zamboanga city.
“I have directed our troops to heighten their alert level, secure all places of worships and public places at once, and initiate proactive security measures to thwart hostile plans,” Defence Secretary Delfin Lorenzana said in a statement.
Pope Francis, the head of the Roman Catholic Church, expressed “the firmest reproach for this episode of violence”.
Yousef Al-Othaimeen, the head of the Organisation of Islamic Cooperation, the world’s largest body of Muslim-majority countries, also condemned the attack, expressing “deep indignation” over the bombings.
Bishop Angelito Rendon Lampon served as a priest at the Cathedral for almost two decades, until his transfer to Cotabato, another city in Mindanao, last week. He said many of his former parishioners were shaken by the attack.
“I know many of the victims because I worked there for 21 years. I am praying for the victims and their families,” Lampon told Al Jazeera.
“We are condemning this attack. Those who are responsible have no respect even for the sanctity of the place,” he said, adding that the priest, who was officiating the mass at the time of the bombing, Fr Ricky Bacolcol, “was still in shock and could not speak about what happened”.
Jolo has long been troubled by the presence of Abu Sayyaf, which has been blacklisted by the Philippines and the United States as a terrorist organisation.
The attack followed Friday’s announcement that the region, a mainly Muslim part of the predominantly Roman Catholic Philippines, had ratified the creation of an autonomous area called Bangsamoro, with 85 percent of voters behind it.
The Bangsamoro, meaning Moro nation, is expected to replace the existing ARMM, which has been criticised as merely nominal, and failed to end the violent conflict that has left at least 120,000 people dead over the past five decades.
Although Sulu, including Jolo, was among only a few areas that rejected autonomy, it will still be part of the new entity when it is fully formed in 2022.
Rebels and the government in Manila hope a new, peaceful Bangsamoro will finally draw the investment needed to pull the region out of the brutal poverty that makes it a hotspot for violence.
Muslim rebels have long been battling for the independence or autonomy on Mindanao, which they regard as their ancestral homeland dating back to when Arab traders arrived there in the 13th century.
With additional reporting by Ted Regencia