Freedom of navigation operations conducted by the US and its allies in the South China Sea have heightened the dilemma faced by Southeast Asian nations caught between China and the United States, diplomatic sources and observers have said.
Many say that the more frequent naval operations by the US and its allies in the contested waters may help reinforce international rules in the face of China's military construction programme in the disputed waters.
But they are not convinced that the operations will be enough to deter China's aggressive territorial claims and smaller countries fear they may pay a price for the US actions.
"Claimant nations other than China are wary of Beijing's activities in the area," said Collin Koh, a research fellow at the S Rajaratnam School of International Studies at Nanyang Technological University in Singapore.
"This concern certainly motivates them to encourage the continued presence of friendly, countervailing powers that can hopefully check Beijing's activities and at least, if not roll back on those activities, to ensure that Beijing is deterred enough to not up the ante with more drastic, escalatory actions aimed at further altering the status quo in the South China Sea."
An Asian diplomat, speaking on condition of anonymity, said the escalating rivalry between China and the US was making it more difficult for his country to remain neutral between the two powers.
"We can't afford to antagonise China. We don't want to be stuck in the middle and be engulfed by the two giants," the diplomat said.
The US remains the most powerful military presence in the Indo-Pacific region, but its activities in the South China Sea mainly take the form of what it calls freedom of navigation operations, in which its warships sail near islands or features claimed by China to indicate its view that they remain international waters.
The US Navy carried out nine such operations in 2017 and 2018. So far this year it has carried out two exercises and has said more are planned.
US Navy Commander Admiral Philip Davidson said last month he expected allies and partners would continue to help the US in the South China Sea "in the months ahead" and that the US was helping the Association of Southeast Asian Nations (ASEAN) in its discussions with China about a code of conduct (CoC), which Beijing has long advocated as a way of reducing the risk of confrontation in the disputed waters.
Jay Batongbacal, an associate professor at the University of the Philippines' college of law, said that while the increasing operations by the US and its allies, including Australia, Britain and France, could help "moderate" some of Beijing's assertive activities, they were unlikely to deter China.
"An ASEAN-US dialogue on the CoC could help identify and clarify points of mutual or convergent or complementary interests in the South China Sea, so that in subsequent negotiations with China, ASEAN could be more conscious of what regional and extra-regional interests to balance in the course of the CoC negotiations," he said.
"It may also provide an opportunity for ASEAN and the US to clarify their respective roles and directions in dealing with China."
But Koh said this would also mean ASEAN nations needed to strike a more delicate balance.
"This may help somewhat, on the assumption that ASEAN countries may at least have extra-regional powers to fall back on and not necessarily have to cave in to Beijing's demands regarding the CoC," he said.
"That said, the ASEAN parties will necessarily have to not only consider the extra-regional powers' commitment to the region - which some may see in the current US administration as possibly tenuous at best - but also their long-term relations with China which is an immediate neighbour and with whom there are considerable economic stakes especially involved."
Beijing regards the naval operations conducted by the US and its allies in the South China Sea as a violation of its territorial sovereignty.
On Thursday, Chinese defence ministry spokesman Ren Guoqiang warned that the military would "take resolute steps to firmly safeguard the sovereignty and safety of the country".
The growing competition between China and the US - which takes many forms, including the trade war and increasingly heated race for technological supremacy - has heightened Southeast Asian nations' fears of being caught in the middle.
Batongbacal said the Philippines, which has competing claims in the South China Sea, was one of the countries that shared this concern.
Tensions between Beijing and Manila reached a peak in the summer of 2016 when an international tribunal judged that China had no historical rights to the South China Sea and ruled in favour of the Philippines, which accused Beijing of seizing the Scarborough Shoal in 2012 after a tense confrontation. The US only expressed support for its long-standing ally two months later.
The incident, Batongbacal said, had "essentially corroborated a popular narrative that the US will only act to protect its own interests and will leave smaller states to fend for themselves".
"Added to this is the fact that these states are also geographically and economically closer to China, and some of them have seen or experienced first-hand how disproportionately aggressive China can be for any perceived slights, they cannot therefore be expected to simply think and act in the same way as Washington," he said.
Philippine officials, including President Rodrigo Duterte, who has favoured a China-friendly foreign policy since taking office in 2016, have publicly questioned whether the US would come to its aid against China.
In an apparent attempt to ease concerns from its allies in the region, US Secretary of State Mike Pompeo said on Friday that the US would support the Philippines under the mutual defence treaty if its forces came under attack in the South China Sea.
Pompeo, who was visiting Manila on his way back from the Hanoi summit between US President Donald Trump and North Korean leader Kim Jong-un, also warned his Philippine counterpart Teddy Locsin to be cautious about Beijing's growing economic influence in the region.
But not everyone is convinced, especially when Southeast Asian economies are highly dependent on trade with China.
"More so if the US cannot provide an effective alternative to China's markets and offers of economic assistance or benefits, which are [regardless of politics] important for all economies in the region," Batongbacal said.
According to a survey by Singapore-based think tank the ISEAS-Yusof Ishak Institute in January, nearly 70 per cent of the 1,008 respondents in Southeast Asia believed US engagement with Southeast Asia was declining while a third said they had little or no confidence in the US as a strategic partner and provider of regional security. In contrast, 73 per cent said China's economic influence reigned supreme in the region.
This article was first published in South China Morning Post.