Three US rubber raiding craft and two small-unit Filipino riverine boats made repeated sallies at a desolate beach at a northern Philippines navy base in a practise stealth landing of squads of armed marines.
Shouting "Volume Fire!" and "Bounce Up", the teams scrambled up the sloping shore with assault rifles to surround a mocked-up enemy tent before running back to their boats in rapid manoeuvres.
"We're here for the sake of training, to build up and develop our capabilities," US Marines spokesman Captain Jeremy Scheier told AFP when asked if they had a specific enemy target in mind.
"There was no specific scenario," he said, adding that Friday's exercises began well before dawn and involved about 40 US and 80 Filipino marines.
About 5,500 US and Filipino forces are taking part in the annual war games over a two-week period.
At the opening ceremony in Manila last week, Filipino Foreign Secretary Albert del Rosario said this year's joint manoeuvres were designed to help the hosts boost their "maritime capability" to address "challenges" in the East Sea.
Philippines Foreign Secretary Albert del Rosario, pictured during a press conference in Manila, on March 30, 2014
The Philippines, which signed a mutual defence treaty with the United States in 1951, has been involved in increasingly tense maritime confrontations with regional power China, which claims most of the sea including waters close to its neighbours.
The United States has said it takes no position in the territorial dispute.
However US President Barack Obama, on a state visit to Manila last week, warned China against using force in territorial disputes and said Washington would support Manila in the event of an attack.
In the latest incident on Tuesday, Filipino police detained a Chinese-flagged fishing vessel and detained its 11 crew members.
It has ignored a Chinese demand to free the vessel and crew.
Philippine military spokeswoman Navy Lieutenant Annaleah Cazcarro said the amphibious landing exercises also involved two Filipino navy ships serving as launch pads about 3.7 kilometres (two nautical miles) offshore.
"This was planned years before," she told AFP when asked if the exercises had any bearing on the latest maritime incident involving China, which the Philippines said occurred near Half Moon Shoal, 106 kilometres west of the large western Philippine island of Palawan.
The Philippines on March 30 filed a formal plea asking a United Nations arbitration tribunal to declare as illegal what Manila said was Beijing's claim to 70 percent of the East Sea.
The seabed in the area is believed to contain huge deposits of oil and gas and the waters straddle vital sea lanes.
Beijing has rejected UN arbitration and urged Manila to settle the dispute through bilateral talks instead.
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