* Apec leaders' summit on November 18-19 in Manila
* Philippines on high alert after Paris attacks
* Trade, economic integration on official agenda
* South China Sea tensions likely to creep into discussions
Reuters/Manila
US President Barack Obama and other world leaders arrived in Manila on Tuesday for the first of two regional summits that were supposed to bolster trade and security ties but have been clouded by the Islamic State threat half a world away.
The Asia-Pacific Economic Cooperation (Apec) gathering on Wednesday and Thursday comes on the heels of a G20 summit in Turkey, which was dominated by discussions about the violence emanating from Syria's 4-1/2-year-old civil war.
Many of the leaders then go on to Kuala Lumpur to attend an East Asia summit at the weekend.
For Obama, the latest flurry of summitry illustrates how his effort to "rebalance" US policy towards Asia-Pacific countries has consistently run into the geopolitical reality that the persistently volatile Middle East cannot be ignored.
The Philippines was on high alert as the leaders arrived. Police in this city of 12mn closed off many roads leading to the venues of the meeting, which will be attended by about 20 heads of state or government, including Chinese President Xi Jinping and Japanese Prime Minister Shinzo Abe.
Philippines officials say there has been no intelligence suggesting there might be an attack on the Manila summit but about 30,000 police and soldiers have been deployed to guard it.
The air force has placed 13 aircraft on standby, most of them helicopters, while the navy has two former US coast guard cutters and a dozen smaller watercraft in Manila Bay.
The USS Fitzgerald, a US navy destroyer, will also be stationed in Manila Bay for the duration of Obama's visit.
As Air Force One was coming in to Manila, two groups of around 100 people each approached the US embassy to stage protests but they were held back by police.
But even before Friday's assault by gunmen and bombers that left at least 129 dead in Paris, there had been concern that Apec's agenda of enhancing economic integration would be undermined by other issues, not least feuding over the South China Sea.
Aides said that on his trip Obama would reassert Washington's commitment to freedom of navigation and overflight in the disputed strategic waterway. As part of that, he was due to tour a coast guard operation in Manila harbour later on Tuesday.
The Philippines has vowed to be a "good host" by keeping the South China Sea off the summit agenda. But the subject has whipped up tension between China and the US in recent weeks, and officials in Manila said it could come up at a concluding retreat of leaders on Thursday.
Not conducive
In Beijing, Vice Foreign Minister Liu Zhemin said China did not want the South China Sea to be the focus of the East Asia Summit in Kuala Lumpur.
"Hyping the South China Sea issue is not conducive to cooperation," Liu said. However, he said it would be hard to avoid and some countries would raise it.
Beijing, which claims almost the entire energy-rich South China Sea through which $5tn in ship-borne trade passes yearly, has stepped up land reclamation and construction in disputed islands and reefs there. Vietnam, the Philippines, Taiwan, Malaysia and Brunei also claim parts of the waterway.
A week before the summit, US B-52 strategic bombers flew near Chinese artificial islands, signalling Washington's determination to challenge Beijing over the disputed sea.
Obama will likely discuss the friction over the South China Sea and military relations when he meets Philippine President Benigno Aquino on the sidelines of the summit on Wednesday.
Aquino and Japan's Abe are also expected to agree on a deal paving the way for Tokyo to supply Manila with used military equipment, possibly including aircraft that could be deployed to patrol the disputed South China Sea, sources said. The deal will mark the first time Japan has agreed to directly donate military equipment to another country.
Manila and Hanoi are due to sign a strategic partnership deal governing how their navies will work together.
Such developments could upset China, which said last week it was up to Manila to repair damaged bilateral ties. Beijing has insisted on using a bilateral track to resolve the dispute.
There was no immediate word if China's Xi would hold bilateral meetings during his visit.
On his three-day trip to Manila, Obama will also meet heads of state of the 12-member Trans-Pacific Partnership group and members of the Pacific Alliance, a Latin-American trade bloc.
