MANILA, Aug. 30 (Xinhua) -- The death toll in Tuesday night's blast in Isulan in the Sultan Kudarat province in the southern Philippines has risen to three, police said on Thursday.

Sultan Kudarat Provincial police chief Noel Kinazo told Xinhua in a telephone interview that the second critically wounded person has also died in a local hospital on Wednesday night, bringing the total death toll to three.

Kinazo said more than 30 people, including two soldiers and a militiaman, were injured when an improvised explosive device rocked Isulan around 8:35 p.m. local time on Tuesday. The homemade bomb was planted under a parked motorbike along a busy highway, he added.

He has earlier said that the explosion occurred while residents are celebrating a local holiday.

The military pinned the blame for the attack on the Bangsamoro Islamic Freedom Fighters (BIFF), a spin-off of the Moro Islamic Liberation Front (MILF) that forged a peace pact with the government.

However, a BIFF rebel denied any involvement in the attack.

Nevertheless, the military and the police are on heightened alert.

"The threat is always there, that is why we are on heightened alert to thwart all hostile plans by the lawless group," said Brig. Gen. Cirilito Sobejana, commander of an Army Infantry Division based in the southern Philippines.

The military said the BIFF has about 300 members.

Established in 2010, the BIFF is among the armed groups in Mindanao in the southern Philippines that pledged allegiance to the Islamic State.