The explosion on Sunday ripped through a gymnasium at Mindanao State University in Marawi City, where pro-ISIL fighters led a five-month siege in 2017 that killed more than 1,000 people.
“The soldiers of the caliphate detonated an explosive device on a large gathering of Christians … in the city of Marawi,” ISIL said in a statement on Telegram.
Philippine President Ferdinand Marcos Jr earlier condemned “the senseless and most heinous acts perpetrated by foreign terrorists”.
Defence Secretary Gilberto Teodoro told a press conference there were “strong indications of a foreign element”.
The United States State Department condemned the “horrific terrorist attack” and said it stood with Filipinos in rejecting violence.
Philippine security officials had suggested on Sunday the attack may have been retaliation for a military operation about 200km (125 miles) from Marawi City that killed 11 Islamist rebels.
On Monday, police said they were investigating at least two people of interest over the bombing.
“In order not to preempt the investigation, we will not divulge the names,” regional police chief Allan Nobleza told GMA News.
Mindanao State University said on Sunday it was “deeply saddened” over the “senseless and horrific act” and had suspended classes until further notice.
Mindanao, an island in the country’s far south, has for decades been racked by violence amid an insurgency by armed separatist groups.
After decades of fighting, Manila in 2014 signed a peace agreement with the Moro Islamic Liberation Front, the largest separatist group, but smaller groups have continued to carry out attacks across the island.
