BEIJING China denounced Vietnam and the Philippines on Monday for getting together on a disputed island in the South China Sea to play soccer and volleyball, calling it "a clumsy farce" and demanded both countries stop causing trouble.
The comments by a foreign ministry spokeswoman were China's first response to the gathering on the Vietnamese-held island of Southwest Cay on Sunday.
Philippine naval officials described the meeting of soldiers from the two sides as a chance to show there can be harmony despite a web of overlapping claims to the potentially energy-rich waters.
"Don't you think this small move together by Vietnam and the Philippines is at most a clumsy farce?" China's Foreign Ministry spokeswoman Hua Chunying said at a daily briefing.
"China has irrefutable sovereignty over the Spratly Islands and the seas nearby," she said. "We demand that Vietnam and the Philippines stop any behaviour that picks quarrels and causes trouble ... and not do anything to complicate or magnify the dispute."
The gathering underscores the growing cooperation between Vietnam and the Philippines, which have both felt China's wrath over the South China Sea, even though both claim Southwest Cay and other islands.
The Philippines, Malaysia and Brunei all claim some of the Spratlys, while China, Taiwan and Vietnam claim the whole chain.
China also claims 90 percent of the 3.5 million sq km (1.35 million sq mile) South China Sea, its reach depicted on its maps with a so-called nine-dash line deep into the maritime heart of Southeast Asia.
Diplomats and experts have described the partnership between Hanoi and Manila as part of a web of evolving relationships across Asia that are being driven by fear of China as well as doubts among some, especially in Japan, over the U.S. commitment to the region.
Separately, China accused Vietnam of ramming its ships more than 1,000 times in a part of the sea and said while it wanted good relations with its neighbour, it would not abandon principles to achieve that.
A Vietnamese fishing boat sank on May 26 during a confrontation not far from where China has towed an oil rig, accompanied by a cordon of Chinese vessels, 240 km (150 miles) off Vietnam.
Last week, Vietnam television broadcast video showed a large Chinese vessel steaming after two Vietnamese fishing boats, then colliding with one which capsized.
The dispute is the most serious deterioration of relations between the Communist states and traditional rivals since a brief war in 1979 following Vietnam's invasion of Cambodia.
Shortly after China brought its oil rig into the area, Vietnam sent a large number of vessels into the area, China's Foreign Ministry said on Sunday.
"There were as many as 63 Vietnamese vessels in the area at the peak, attempting to break through China's cordon and ramming the Chinese government ships for a total of 1,416 times," the ministry said.
"China exercised great restraint and took necessary preventive measures."
China has communicated with Vietnam more than 30 times, asking it to "stop its illegal disruption", the ministry said.
"China wants good relations with Vietnam, but there are principles that China cannot abandon."
Scores of Vietnamese and Chinese ships have squared off around the rig since the platform was towed to the area in early May.
The Haiyang Shiyou 981 rig is drilling between the Paracel islands occupied by China and Vietnam. Vietnam says the rig is in its 200-nautical mile exclusive economic zone and on its continental shelf. China says it is operating within its waters.
The rig's deployment set off anti-Chinese riots in Vietnam last month in which at least four people were killed.
(Adds dropped words "Foreign Ministry" in paragraph 14)
(Additional reporting and writing by Sui-Lee Wee; Editing by Robert Birsel)