MANILA - A bomb blast killed one person and injured 15 in an internet cafe in the southern Philippines on Sunday, in the second such attack in days blamed by the military on pro-Islamic State militants.Isulan, a mostly Christian city on southern Mindanao island, was placed on lockdown to hunt down those behind the attack, Brigadier General Cirilito Sobejana, an army division commander, told reporters.No group claimed responsibility."Most likely it's still the Bangsamoro Islamic Freedom Fighters (BIFF)," the commander said."There is no other group who would dare to carry out the bombing and there is no other group with an interest to bomb without any reason."The BIFF were also blamed for a blast on Tuesday about 500 meters away which killed three people and wounded more than 30.Mindanao has a large Muslim minority. The BIFF is a breakaway faction of a Muslim separatist group which signed a 2014 peace deal with the government to end 50 years of conflict that had killed 120,000 people and displaced 2 million in the south of the mainly Catholic Philippines.