The Philippines Government has tightened security in Zamboanga City after an improvised bomb exploded at the arrival area of Zamboanga International Airport on 5 August.
The blast, which occurred at 6.15pm, killed two people and injured 21 others, according to Sulu Governor Abdusakur Tan.
The development also prompted US Ambassador Harry Thomas to cancel his visit to the city.
Zamboanga City police chief senior superintendent Edwin de Ocampo said that because the airport's closed-circuit television has no recording capability, police are unable to scan footage for evidence.
The airport is located near the headquarters of US troops who are assisting the Philippines military in its anti-terror drive in Mindanao, one of the strongholds of the Al Qaeda-linked Abu Sayyaf terrorist group.
The US Embassy offered its help in the investigation of the incident, according to gmanews.tv.