US Embassy spokeswoman Karen Kelley said the bombing prompted the embassy to review its security posture, while 260 US Special Forces deployed in Mindanao for a humanitarian mission in the island province of Basilan were placed on high alert.
"It is a terrible incident," Kelley said.
US army Capt. Catherine Morelle-Oliveira, spokeswoman for the US contingent in Mindanao, said they grieved for the death of Sgt. Mark Jackson, but added they would continue with their mission "in support of Operation Enduring Freedom in the southern Philippines."
The embassy continued to advise all American nationals to exercise caution while staying in the Philippines, and reiterated the warning to avoid traveling to the southern and western areas of the country "because of the Abu Sayyaf and kidnap-for-ransom groups that had abducted and killed foreign nationals."
At Malacañang, President Arroyo condemned in the strongest terms yesterday the Zamboanga attack.
National Security Adviser Roilo Golez expressed the sentiments of Mrs. Arroyo who had a sore throat, in deploring the bomb attack.
"Of course we condemn this senseless act of violence and we extend our heartfelt condolences to the family of the US serviceman," Golez said, adding that they have officially notified the families of the American victims.
"You know it’s a tragedy to die. It’s a greater tragedy to die in a strange place thousands of miles away from home and it is indeed a very tragic and very treacherous act on the part of the perpetrator," he said.
Kelley said they could not say if the Americans were the actual target of the bomb attack in Zamboanga.
Opposition Sen. Rodolfo Biazon, himself a former Armed Forces chief, also deplored the attack as a "cowardly act of terrorism."
"Philippine authorities should conduct a thorough investigation to find out the perpetrators of this terrorist act and bring them to justice. But it must be clear that any action against them must be under the direction and initiative of the Philippine government," Biazon said in a statement.
At the same time, Biazon suggested that the American troops should be confined to barracks to prevent further attacks.
"Allowing them to roam outside their camps would just make them irresistible targets for terrorists and make matters more complicated for the Philippines if they incur casualties again. We do not want this to escalate into a situation where the United States will justify military action in the Philippines."
Meanwhile, US soldiers virtually took over security matters at Camp Enrile and at a military hospital at the Southern Command headquarters following the bomb attack.
A Filipino senior military officer involved in camp security viewed the Americans’ intervention as an insult to the Filipino soldiers and a breach of security protocol.
Oliveira said, however, that there has been no change in their security plans. "We are instituting the force protection measures and that has been going on throughout," she said.
In another development, police and military bomb disposal experts safely detonated on Wednesday another powerful home-made bomb planted under a town plaza stage in Midsayap, North Cotabato.
The incident came two days after two grenade blasts rocked nearby Pikit and Kabacan towns in the same province.
Midsayap police director Inspector Julie Amanon said the bomb was discovered by local residents who reported it to the police.
It was the seventh foiled bombing attempt in Midsayap, police said.
An unidentified man reportedly tossed a grenade through an open window of the house of Nor Panabilan, a farmer, who was wounded in the blast.
In the second incident, motorcycle-riding men hurled a fragmentation grenade into a vehicle owned by the town’s former vice mayor, Cedric Mantawil, seriously wounding his parents, Maniaga and Soraida Mantawil. — With Roel Pareño, John Unson, Marichu Villanueva, AFP report