Tensions in the South China Sea are rising, pitting China against smaller and weaker neighbors that all lay claim to islands, coral reefs and lagoons in waters rich in fish and potential gas and oil reserves. China's recent construction of artificial islands in the Spratly archipelago, complete with airstrips and radar stations, and U.S. patrols challenging Beijing's vast territorial claims, have caused concern that the strategically important waters could become a flashpoint.
A look at some recent key developments:
CHINA DEFENDS MILITARY PLANE LANDING
China says the United States is overblowing a humanitarian emergency mission that involved one of its military planes landing on an artificial island — which also happens to be one of three recently built military outposts with long runways.
The Y-8 transport aircraft made a trip to Fiery Cross Reef in the Spratlys to evacuate three injured construction workers, according to the Ministry of Defense.
State Department spokesman John Kirby questioned the need for a military aircraft, citing concern that China keeps militarizing the disputed region. He said the injured workers were involved in infrastructure improvements of a military nature.
"One could argue that it's just another sign that the Chinese are willing to keep militarizing the effort in general," he told reporters.
China's Defense Ministry said it was completely within the mission of the People's Liberation Army to rescue people — and carry out construction activities and deployment of defense facilities on related islets and reefs in the Nansha Islands, the Chinese name for the Spratlys.
Filipino fishermen say they've seen more Chinese coast guard ships than usual around the contested Scarborough Shoal, which China effectively took over in 2013 after a tense standoff with Philippine vessels.
Although fishermen have been complaining they're being driven away by Chinese ships, the Philippine Department of Defense said it could not confirm an increase in Chinese presence at the shoal, 145 miles (230 kilometers) from Luzon island.
Meantime, the U.S. Air Force flew its first mission over the Scarborough area as part of a new Air Contingent force stationed in the Philippines. It involved four A-10C Thunderbolt jets and two Sikorsky HH-60 helicopters.
The mission: establishing air and maritime "domain awareness" and "assuring all nations have access to air and sea domains throughout the region in accordance with international law," according to a U.S. military statement.
Free navigation "is extremely important, international economics depends on it — free trade depends on our ability to move goods," said Col. Larry Card, commander of the Air Contingent, part of stepped-up U.S. assistance to its Philippine ally.
As China and other claimants await the ruling of a U.N. tribunal on a case filed by the Philippines that challenges Beijing's vast territorial claims, world and regional players are lining up behind one side or the other.
China has refused to take part in the proceedings at the U.N. Court of Arbitration, and it's not clear how the ruling can be enforced.
Russian Foreign Minister Sergey Lavrov, meeting with his Chinese counterpart in Moscow, said Russia is against any interference from third parties — a reference to the U.S. — " or any attempts to internationalize these disputes."
Russia repeated China's position that "only parties can resolve their dispute through direct talks."
Britain, on the other hand, says it will stand alongside the U.S. in supporting the ruling.
Hugo Swire, British minister of state for the Foreign Office, told a Washington think tank that growing tensions in the South China Sea are driven by China's assertive actions. He said any ruling by the court should be binding on both parties.
In Southeast Asia, which is broadly divided between pro- and anti-China blocs, Chinese Foreign Minister Wang Yi said Beijing had reached a consensus with Brunei, Cambodia and Laos — its traditional allies — on the South China Sea issue.