As tensions in the South China Sea dispute degenerate into the most serious crisis in years, the 60-year-old security treaty binding the United States to the Philippines, its former colony, is under scrutiny. Manila officials are putting counterparts in Washington under pressure for a robust rhetorical response to what they describe as a string of recent incursions by China as it asserts sovereignty within its controversial nine-dotted line that claims virtually the entire South China Sea. But, so far at least, US officials are stopping short of outlining precisely what the 1951 Mutual Defence Treaty requires in the still-unlikely event that current tensions spiral into a naval clash between China and the Philippines - even as they expand naval deployments in the area. 'There is a strategic ambiguity on the part of Washington as to whether the Philippines' claims to the Spratly Islands fall within the treaty,' said Ricki Carandang, a spokesman for Philippine President Benigno Aquino. 'But we believe that there are areas of concern - such as the Reed Bank and nearby Amy Douglas Bank - that are not in dispute and are not part of the Spratlys.' Manila has accused Chinese vessels of placing construction material on the unoccupied Amy Douglas Bank, near Palawan, last month in one of six incursions since February. Officials on Wednesday said the Philippines navy had removed wooden posts and markers from Reed and Amy Douglas as well as Boxall Reef in the Spratlys. They did not specify which country had put them there. Aquino has said his nation needed US help, while his defence secretary Voltaire Gazmin has urged Washington to use its full 'persuasive power' to help keep the peace - comments which have resonated in Beijing, where officials have repeatedly warned against any moves by Vietnam or the Philippines to 'internationalise' the dispute. The situation is also being closely watched in the region as a signal of Washington's commitment to backing for allies and partners in times of trouble. Washington's position over the treaty stands in contrast to its support for Japan at the height of SinoJapanese tensions over the disputed Diaoyu/Senkaku islands last year. When Washington announced that the island did in fact come under the US-Japanese security treaty, the penny dropped in Manila: Would the US say the same over the Philippines' claims in the South China Sea? The US-Japanese treaty of 1960, however, is far more explicit about covering areas under Japanese administration. When asked about the treaty, US officials say that Washington is concerned about the situation but does not take sides in regional territorial disputes. Harry Thomas, US ambassador to the Philippines, stressed the strategic nature of the relationship in a speech this week but again stopped short of specifics. 'The Philippines and the US are longstanding treaty allies. We are strategic partners. We will continue to consult each other closely on the South China Sea, Spratly Islands and other issues,' he said. Singapore-based security scholar Ian Storey said the US faced a dilemma should violence ever break out. 'On the one hand, the Spratlys are not included, yet the US does have obligations if the armed forces of the Philippines are attacked to at least consult on what steps should be taken next,' he said. 'I think it is safe to assume that Washington is looking at this very closely, indeed... it is not just a question of the Philippines nowadays, it is an issue that speaks to its role in the wider region - and they know they can't ignore that.'