The Chinese vessels later left without confrontation, said Philippine military commander Lt. Gen. Juancho Sabban.

The incident happened Wednesday at the Reed Bank, which is near the disputed Spratly Islands that are claimed by the Philippines, China and other nations, said Sabban, who heads the military’s Western Command. Philippine officials said the Reed Bank is clearly within Philippine territory.

The Philippine government asked the Chinese Embassy to explain, presidential spokesman Ricky Carandang said.

“The boats approached in a way that the Philippine vessel thought it was better to back off,” Carandang told The Associated Press.

Chinese Embassy spokesman Ethan Sun declined to immediately comment.

The Spratlys, a group of islands, reefs and atolls believed to be sitting stop vast oil and gas reserves, has been claimed in whole or in part by China, Brunei, Malaysia, Taiwan, Vietnam and the Philippines. It has long been regarded as a potential flash point for conflict in Asia.

Sabban said he deployed an OV-10 bomber plane and an Islander light aircraft to the Reed Bank to undertake surveillance after the Philippine ship radioed his command that two suspected Chinese patrol boats approached and ordered it to leave the area.

When the planes reached the area, the foreign vessels have left, he said.

“It’s clearly our territory,” Sabban told the AP. “If they’ll bully us, well, even children will fight back.” The vast sea area where the incident happened lies more than 200 kilometers west of the southwestern Philippine province of Palawan.

Aside from its potential oil deposits, the Spratly archipelago has rich fishing grounds and straddles busy sea lanes that are a crucial conduit for oil and other resources fueling China’s fast-expanding economy and those of other Asian nations.

Beijing reacted with fury last year when US Secretary of State Hillary Clinton told an Association of Southeast Asian Nations regional security forum in Vietnam that the peaceful resolution of disputes over the Spratly and Paracel island groups was in the American national interest.

Beijing said Washington was interfering in an Asian regional issue.

The United States worries the disputes could hurt access to one of the world’s busiest commercial sea lanes.

President Barack Obama and ASEAN heads of state have reiterated their support for a peaceful resolution of the disputes, freedom of navigation and respect for international law in the South China Sea.