While Southeast Asian nations have repeatedly warned against being forced to choose between China and the US, the past few days have only confirmed that the strategic rivalry now reaches deep into the political heart of the region. The historic failure of Asean foreign ministers to agree on the wording of a routine communique mentioning the South China Sea is one symbol; increased Sino-US commercial competition over Myanmar and Cambodia - for decades a blood-soaked proxy battlefield for superpowers - is another. The failure over the communique is particularly dramatic. And it is producing fears that it could yet poison upcoming talks with China over a long-awaited code of conduct to govern disputes in the South China Sea. It produced open tensions yesterday as the top envoys of Cambodia, the meeting host, and the Philippines took pot-shots at each other - a highly rare event given the Association of South East Asian Nations faith in consensus, and tradition of keeping fights 'within the family'. Cambodian Foreign Minister Hor Namhong said he regretted the discord, but he 'could not accept that the communique had become hostage of the bilateral issue (between the Philippines and China)' - echoing earlier language from Beijing. For several days ministers had argued in private over a Philippines demand to include a reference to its standoff with China over the Scarborough Shoal, known in Chinese as Huangyan. A range of diplomats said discussions were at times fierce, but consensus was eventually close, apart from the concerns of the chair Cambodia - prompting internal accusations that it was representing China's views, not Asean's. A Philippines Foreign Ministry statement 'deplored' the unprecedented failure, noting the fact that every other foreign ministers meeting in 45 years of the grouping had produced a communique. It took 'strong exception' to Cambodia for opposing mention of the shoal, saying that divisions undercut previous Asean agreements on tackling disputes as a unit, 'and not in a bilateral fashion - the approach which its northern neighbour [China] has been insisting on'. Just ahead of the meeting, Foreign Ministry spokesman Liu Weimin said the South China Sea was an issue between China and individual Asean members, adding that the wider Sino-Asean relationship must not be held 'hostage'. Yesterday Liu called the meeting 'productive', adding that 'China's views and position on many issues has won the appreciation and support of many participating countries'. In the closed-door meeting on Thursday, Foreign Minister Yang Jiechi spoke of how the presence of a Philippines naval ship at Huangyan had caused concern and indignation among Chinese people. He told the Philippines side to 'face the facts squarely and not to make trouble', Xinhua reported. Some Asean diplomats said the current divisions could serve China's purposes - and reflected a strong behind-the-scenes lobbying campaign to weaken a united Asean role over the South China Sea. 'If it is a victory, it is only a partial victory,' one senior envoy from a non-claimant Asean state said. As late as 2009, Chinese lobbying and pressure had successfully kept the South China Sea off the agenda - now it remained firmly an issue of regional concern, despite the latest hiccup. 'If they are ever going to completely shut down Asean like before, they must fight uphill - it is on the agenda, and that's the bottom line,' the diplomat said. Ongoing US involvement in the issue, both publicly and privately, is a key factor in that - something China is actively resisting. The two powers now appear, once again, in open competition over Cambodia. While billions in Chinese investment, aid and loans has bankrolled much of the war-torn nation's recent commercial development, US Secretary of State Hillary Clinton appears determined for the US to play catch up. Yesterday she hosted the biggest ever gathering of US investors inside the country - an event to which the Thai and Myanmese Prime Ministers were also invited. She also unveiled a major new aid programme for the region - the Asia Pacific Strategic Engagement Initiative - but has yet to detail its size or scope. And while Chinese-Asean trade now dwarfs US commerce, she has also been stressing figures showing that US business has invested more than three times as much in Southeast Asia as China. Like the wider rivalry, however, that figure can be expected to change over time.