Two terror attack suspects have confessed to involvement in separate blasts the killed 38 people in the Philippines, prosecutors said Saturday.

Tohami Bagundang and Jimmy Balulao were arrested Wednesday along with three others in connection with the bombings in Davao city and its airport. All five face murder charges.

Davao prosecutor Danilo Belo said Balulao, 17, admitted planting an explosive in the airport March 4 that killed 22 people, including an American missionary, and injured more than 100.

Belo said that Bagundang, 19, confessed to the April 2 blast at a ferry passenger terminal, killing 16 people and injuring 55. Bagundang said he was told by To Akmad, another of those arrested, to place a bag containing the bomb under a table. Belo said he claimed he saw Akmad detonate the device.

Both Balulao and Bagundang said a fourth man arrested Wednesday, Esmael Mamalangkas, promised them nearly $1,000 each to carry out the attacks.

Despite the arrests, the motives behind the attacks remained unclear. The government has blamed the Muslim separatist Moro Islamic Liberation Front, but the group has denied the charges.

Prosecutor Augusto Gonzales said a further checks of two suspects in the airport bombing, Terso Sudang and Undungan Sudang, revealed "serious doubt" about their involvement.

The bombings came amid debate over the role of U.S. troops in anti-terrorism efforts in the Philippines, where Muslim insurgents, including a group believed linked to Al Qaeda, have battled the government for decades.

U.S. troops currently train Philippine forces but do not engage in combat. U.S. defense officials announced earlier this year they had an agreement to deploy more than 1,000 troops on the nearby island of Jolo to launch joint operations that could draw them into combat. But the offensive was put on hold after the Philippines balked, saying its constitution bars foreign troops from fighting in the country.