MANILA -- The Al-Qaeda-linked Abu Sayyaf rebel group on Wednesday claimed responsibility for a deadly bomb attack in the southern Philippines that killed 23 people, but called the civilian carnage a mistake, DPA reported.

Amid the investigation into the bombing of the Davao International Airport on the southern island of Mindanao, another bomb ripped through a shopping mall in Cotabato city Wednesday afternoon.

Police said at least 12 people were injured in a stampede as shoppers and employees rushed out of the southeast department store after the blast in the men's section of the store.

In a telephone interview with local reporters on Wednesday, Abu Sayyaf commander Hamsiraji Sali apologized to the families of the victims in Tuesday's bombing at the airport in Davao city, 990 kilometers south of Manila. "We are sorry that many civilians were killed, that was not the intention," he said. "Our target was the Davao Airport and the plan was for the bomb to explode in the night when there were few people in the terminal."

Sali said his men erred in planting the bomb, adding the plan was to sabotage the economy, and not to harm innocent civilians.

Police said the bomb was placed inside a knapsack and left at a crowded waiting area for people welcoming arriving passengers.

Government and military officials, however, refused to accept Sali's claim, and appeared inclined to blame the separatist Moro Islamic Liberation Front (MILF) for the bombing.

Police said nine suspected MILF rebels were arrested overnight, and were being interrogated for their possible involvement in the attack.

The military also blamed Wednesday's bombing on the MILF, the largest Muslim rebel group fighting for a separate Islamic state on Mindanao, which recently mounted attacks to retaliate against a major offensive against its stronghold last month.

Defense Secretary Angelo Reyes said the MILF and the Abu Sayyaf could be working together. "It's possible that this is a set play," he said. "In other words, the MILF is asking the Abu Sayyaf to own up to this dastardly act so that it could retain whatever respectability it still has." Davao city mayor Rodrigo Duterte added he does not make any distinction between the two groups, saying, "I think they are one group, almost the same, similar crimes, similar modus operandi."

Abu Sayyaf commander Sali said the arrests were "useless" since he already has custody of the bombers. He said the Abu Sayyaf would punish the bombers for their mistake. "We will study the Qoran for what punishment must be meted on them," he said. "If they must be executed, then we will execute them based on the laws of the Abu Sayyaf and the Qoran."

The death toll in the Davao Airport bombing rose to 23 on Wednesday, after two injured victims succumbed to injuries. Doctors at the state-run Davao Medical Center said 15 others were still in critical condition.

Among the fatalities was 59-year-old American missionary William Hyde, who had been staying in Davao for the past seven years with his wife Lyn.

American Barbara Stevens, her 10-month-old son Nathan and four-year-old daughter Sarah were among the more than 140 injured victims, police said. Her husband, Mark, was unhurt but in shock.

The Hydes were at the airport to welcome the Stevens, who were on a visit.

The Air Transportation Office (ATO) said the Davao International Airport reopened on Wednesday morning, with domestic carriers Cebu Pacific and Air Philippines resuming commercial flights. But flag carrier Philippine Airlines has yet to resume its flights.

The ATO ordered stepped-up security in other airports in the country, particularly the international airport in Manila, where up to 400 additional policemen were deployed to augment existing security forces.

U.S. President George W. Bush condemned the Davao Airport attack, which occurred amid negotiations between Manila and Washington for a joint antiterrorism mission against Abu Sayyaf rebels on their stronghold Jolo island.

Days before the Davao Airport bombing, Sali warned the Abu Sayyaf would mount attacks to create trouble on Mindanao.

The United States has included the Abu Sayyaf on its blacklist of foreign terrorist organizations and indicted several leaders, including Sali, for kidnapping three Americans in 2001, two of whom were killed in captivity.