U.S. Embassy spokeswoman Bettina Malone said the BQM-74E drone was launched from the USS Chafee, a guided-missile destroyer, as a mock missile target during naval combat exercises off Guam's coast in September.
The Philippine navy deployed a ship with ordnance experts after a diver and fishermen who found the drone over the weekend reported it may have been a bomb. The discovery sparked concerns because U.S. troops are allowed to engage in exercises with local troops but are legally barred from engaging in combat operations in the country.
A joint commission overlooking annual combat exercises by U.S. and Philippine troops as well as American ship visits has been asked to look into the drone's discovery.
Sen. Loren Legarda, who heads the Philippine Senate committee on foreign relations, asked the commission to check if any of the rules governing visits by American forces in the country had been breached.
The drone's discovery in Philippine waters "raises a serious concern of national security," Legarda said.
Department of Foreign Affairs spokesman Raul Hernandez said the Philippine government has been assured by the U.S. Embassy "that the reported aerial vehicle is by design and purpose solely used for target practice and not armed or used for surveillance."