Three Americans - a Southern Baptist missionary and her two children - were among the wounded. Many of the injured were in serious condition, and officials feared the death toll could rise. The dead included a boy, a girl, 10 men and seven women. 

The attack came at a time of debate over the mandate of 1,000 troops the United States has offered to send to the Philippines to help fight another violent Muslim group. The deployment was put on hold after many Filipinos objected to the troops having a combat role. 

MILF spokesman Eid Kabalu denied his group was responsible. He condemned the attack and said the MILF was ready to cooperate in an investigation. 

A statement from President Gloria Macapagal Arroyo said police detained "several men" in connection with the blast. Arroyo said she ordered police and the military "to hunt down the bombers and their accomplices." 

In Washington, White House spokesman Ari Fleischer said the explosion had "all the earmarkings of terrorism." 

"The president condemns the bombing in the Philippines this morning. We are working closely with the Philippine government, which has fought valiantly in the war on terror," Fleischer told reporters. 

A civil defense spokeswoman in Davao, Susan Madrid, said the explosion occurred at 5:20 p.m. local time as dozens of people waited for a plane to arrive. 

"I saw bodies flying," Terry Labado, an airport official said. 

"We rushed out of the building to see where the explosion happened. We saw many dead." 

An airport security official, who did not want to be identified, said the bomb rocked the front of the terminal building, smashing windows and causing considerable damage. TV footage showed the waiting stand in front of the terminal building wrecked by the blast, and pieces of metal strewn on the road. 

"It happened ... a few minutes after a Cebu Pacific flight arrived and people packed the waiting area. There were many people killed. I saw six persons killed on the spot," the official said. 

National Police Deputy Chief Edgar Aglipay told a Manila radio station that the explosion was caused by a bomb hidden inside a backpack. 

Madrid said 18 people were killed and 147 were injured. One hospital alone reported 91 casualties. In addition to the 18 others killed, an American also died, the American Embassy said. 

The Southern Baptist Convention's International Mission Board in Richmond, Va., confirmed that its missionary William P. Hyde, 59, of Cedar Rapids, Iowa, died in surgery from severe head and leg injuries. Hyde was meeting other Southern Baptist missionaries at the airport as they returned from a family trip. 

Missionary Barbara Wallis Stevens, 33, of Willard, Mo., was slightly injured and her son Nathan, 10 months, was hit by shrapnel in the liver. She said her daughter Sarah also was injured but released after treatment. Her husband escaped injuries. 

Stevens - a church and home outreach worker - said in a telephone interview from the hospital that her family had just arrived from Manila when the bomb went off. 

"I just heard it explode to my side," she said. "I was carrying my infant son so I grabbed my daughter and picked her up and ran away. I was afraid there could be more bombs." 

"Our hearts go out to these families and their coworkers," said a statement issued by Southern Baptist spokesman Larry Cox. "We are moving quickly to assist the missionaries affected by this tragedy." 

Hyde worked in church leadership development. He and wife Lyn have two grown sons. 

Davao Mayor Rodrigo Duterte ordered all pharmacies and drug stores to remain open to supply medicine to the victims. Flights to and from Davao were suspended. 

Arroyo called an emergency meeting of the Cabinet oversight committee on internal security later Tuesday. She said the bombing was "a brazen act of terrorism which shall not go unpunished." 

In a separate incident Tuesday, an explosion in Tagum, north of Davao, injured two people, said military spokesman Lt. Col. Daniel Lucero. He gave no other details. 

The Moro rebels have been fighting for a separate Muslim homeland in the impoverished southern Philippines for three decades. Despite a 1997 shaky cease-fire, fighting has occasionally flared up. 

American troops went to the Philippines last year as their first expansion of the war on terrorism outside the fight with al-Qaida in Afghanistan. Some 1,200, including 160 Special Forces, were sent to the country in what officials said was a mission to "train, advise and assist" Filipino forces battling Abu Sayyaf guerrillas on the neighboring island of Basilan. 

Last month, U.S. defense officials announced they had an agreement to deploy more than 1,000 U.S. troops in an effort to rout Abu Sayyaf forces, a group from the island of Jolo. But the offensive was put on hold after Pentagon officials described the deployment as "joint operations" that would have drawn Americans into battle. 

That wording caused an uproar in the Philippines. Newspapers, lawmakers and left-wing groups accused the government in Manila of violating the constitution that bars foreign troops from combat. Manila repeatedly denied there would be a U.S. combat role, saying Americans were coming for a training exercise.