Tensions in the South China Sea are rising, pitting China against smaller and weaker neighbors who 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 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 of the most recent key developments:
EDITOR'S NOTE: This is a weekly look at the latest key developments in the South China Sea, home to several territorial conflicts that have raised tensions in the region.
INDONESIA, MALAYSIA WORRIED
Vietnam and the Philippines have been China's most frequent South China Sea adversaries, but now Indonesia and Malaysia are upset over forays by Chinese vessels close to their shores.
Tensions with Indonesia flared when one of its patrol ships intercepted a Chinese fishing vessel on March 19 off the Natuna Islands. That's where Indonesia's exclusive economic zone overlaps with China's so-called "nine-dash line" — which outlines Beijing's vast claims to almost the entire South China Sea.
According to Indonesian officials, a Chinese coast guard vessel came to the rescue of the fishermen and deliberately rammed the boat as it was being towed, allowing it to escape.
Indonesia has since refused Chinese demands to release eight crewmen who are being held on charges of illegal fishing. Indonesia deployed four special forces units equipped with an advanced air defense system to the largest of the Natuna Islands, according to IHS Jane's Defence weekly.
Achmad Sukarsono, an analyst at Eurasia Group, said the skirmish could signal a turning point in Indonesian views on the South China Sea. It has "dispelled the notion in Jakarta that Indonesia has no real stake in South China Sea tensions," he said.
Malaysia, meanwhile, complained that about 100 Chinese fishing boats had encroached near the Loconia Shoals. The Chinese Foreign Ministry said the boats have a right to be there. Chinese officials consider the waters to be traditional Chinese fishing grounds.
PHILIPPINES, U.S. TROOPS IN WAR DRILLS
The Philippines, which has turned to the U.S. to beef up its defense against China, has hosted more than 5,000 American troops for annual war games that include a scenario that could be playing out in the South China Sea.
A key exercise involves U.S., Australian and Philippine forces retaking an oil rig seized by hostile units. The mock assault utilizes an unused rig off the western province of Palawan, which faces the South China Sea.
A highly mobile U.S. rocket system, the M142 HIMARS, is being used for the first time in the Philippines during the exercises. U.S. Defense Secretary Ash Carter will witness the drills when he visits this week.
The Philippines is expecting soon a ruling at a U.N. tribunal on its case challenging China's maritime claims. China has refused to take part in the proceedings and said it would not be bound by the ruling.
OIL RIG MOVES CLOSER TO VIETNAM — AGAIN
Tensions between Vietnam and China are heating up again.
Vietnam has demanded that China remove an oil exploration rig from an area of the South China Sea where their border is still being demarcated, and has lodged a protest with the Chinese Embassy in Hanoi.
The oil rig was at the center of a standoff in 2014 when China parked it near the Paracel islands, which Vietnam claims as its exclusive economic zone. The incident sparked deadly riots in Vietnam targeting Chinese-owned companies.
Vietnam Foreign Ministry spokesman Le Hai Binh also protested China's operation of a new lighthouse on Subi Reef in the Spratlys, which is also claimed by Vietnam, the Philippines and Taiwan.
Rejecting Vietnam's demands, Chinese Foreign Ministry spokesman Hong Lei said the oil rig is conducting standard exploratory activities within waters under China's "undisputed" jurisdiction.
Hong also said the lighthouse on Subi Reef is a matter falling within China's sovereignty.
U.S. ADMIRAL REPORTEDLY WANTS MORE AGGRESSIVE APPROACH
Adm. Harry Harris, commander of the U.S. Pacific Command, reportedly wants a more robust approach to China, including more assertive freedom-of-navigation operations such as helicopter flights and intelligence-gathering within 12 miles (19 kilometers) of Chinese-controlled features.
So far, U.S. Navy ships have twice sailed close to Chinese-controlled islands. However, critics say those maneuvers amounted to innocent passage, during which foreign vessels do not stop or carry out activities that might be perceived as hostile.
The Navy Times quoted defense officials as saying the White House is discouraging strong rhetoric by military leaders on the South China Sea. It reported that National Security Adviser Susan Rice on March 18 imposed a gag order on military leaders over South China Sea comments in the run-up to the nuclear summit in Washington that ended April 1.
"The White House's aversion to risk has resulted in an indecisive policy that has failed to deter China's pursuit of maritime hegemony while confusing and alarming our regional allies and partners," Sen. John McCain, chairman of the Senate Armed Services Committee, said in a statement.
Harris declined to comment on the report, according to the Navy Times.
Chinese President Xi Jinping, speaking in Washington, said that Beijing respects freedom of navigation and overflight but will defend its sovereignty in the South China Sea. Xi said China won't accept any act disguised as freedom of navigation that violates its security.
"Washington should know that the more provocative moves it makes against China, the more counter-measures Beijing will take. Such an undesirable cycle may push both sides nearer confrontation and cause both to prepare for the worst-case scenario, potentially making it self-fulfilling." — editorial in the U.S. edition of the state-supported China Daily.
Associated Press writers Hrvoje Hranjski in Bangkok, Jim Gomez in Manila, Philippines, Christopher Bodeen in Beijing, Tran Van Minh in Hanoi, Vietnam, Eileen Ng in Kuala Lumpur, Malaysia, and Niniek Karmini in Jakarta, Indonesia, contributed to this report.