Police said Friday they will charge leaders of a Muslim separatist group in an airport bombing that killed 21 people, despite rebel denials of involvement.

In fresh violence, police said one man was killed and two people were hurt Friday when a homemade bomb constructed from a mortar exploded prematurely in Tacurong city in Sultan Kudarat province, about 95 miles southwest of Davao.

Police said the suspected bomber, Sami Abubakar, 27, died of injuries after the bomb went off under the seat of his motorcycle. Two female high school students were also seriously injured.

Authorities investigating Tuesday's explosion at Davao airport said the alleged bomber, a 23-year-old man who was among those killed, was a member of the separatist Moro Islamic Liberation Front.

MILF Vice Chairman Al Haj Murad insisted his group was not responsible and asserted that the bombing, which killed an American missionary, was a ploy by the military to justify deployment of U.S. troops to fight Muslim rebels.

Police Chief Supt. Isidro Lapena, one of the investigators, said "personalities and the leadership of the MILF" would be charged.

The MILF has been fighting for Muslim self-rule in the predominantly Roman Catholic Philippines for more than three decades.

President Gloria Macapagal Arroyo has proposed a peace agreement with the MILF, but the rebels have accused the government of negotiating in bad faith. In a major offensive last month, government troops overran a key MILF stronghold on Mindanao island, and the rebels responded with stepped-up attacks on army positions and explosions at power pylons and a bridge.

Local authorities said the MILF rebels on Thursday blew up a bridge under construction about 559 miles south of Manila, injuring two workers.

On Friday, dozens of grieving relatives of victims held prayers at the site of the airport bombing, carrying placards that denounced the "satanic bombing" and called on the government to "wipe out" rebel groups.

The bombing occurred amid political and public debate in the Philippines over the role of U.S. troops training Filipino soldiers in counterterrorism. The United States wanted about 1,000 U.S. troops, set for deployment on southern Jolo island later this year, to be allowed into combat against the Muslim Abu Sayyaf group. But Arroyo on Wednesday ruled out a combat role, saying the Americans would only train and assist Philippine troops.