The U.S. government is currently investigating the death of an American serviceman, who was killed on Tuesday in a landmine explosion in Indanan, Sulu, a stronghold of extremist Muslim militants in Southern Philippines.
U.S. Embassy spokesperson Rebecca Thompson declined to give details when sought for reaction.
"We're investigating the incident," Thompson said in a text message.
Three Filipino soldiers, who were on board an American Hummer jeep with the U.S. serviceman, were also injured.
No group has claimed responsibility for the attack, the military said.
The presence of American troops in Mindanao since 2002 has fanned speculations that they are involved in combat operations against Al-Qaida-linked terrorists in Mindanao like the Abu Sayyaf, which is on the U.S. government's list of the foreign terrorist organizations.
A New York Times report last month revealed that at least 600 American troops under the Joint Special Operations Task Force-Philippines (JSOTF-P), headquartered in the Philippine military camp in Camp Navarro in Zamboanga City, have remained in the country and have been using the Visiting Forces Agreement (VFA) as a means to stay.
The report has instigated calls in the Philippine Senate for the termination of the VFA.
Last week, the government announced that it will conduct a review of the controversial 10-year-old visiting forces pact with Washington, which will be the basis for its decision on whether or not to terminate the accord.
An inter-agency and multi-disciplinary study group will conduct the review "as soon as possible."
The reviewing panel, the government said, would come up with recommendations that will be the basis for a renegotiation of the accord.