For more than two decades, China's foreign policy has been low-profile, following a famous dictum by late leader Deng Xiaoping, who urged his countrymen to 'hide your brightness, bide your time'. But now, under a new communist maxim of 'advance with the times', China's leaders seem to be fine-tuning their approach, as increasing wealth and power emboldens the country on the world stage. The latest tit-for-tat war of words over what is called 'national interests' between top diplomats of China and the United States at the recent Asean Regional Forum in Hanoi, Vietnam, and the high-profile joint military exercises by US and South Korean forces and drills by the People's Liberation Army in the northeast Asian region suggest that Chinese diplomacy has gradually moved from advancing with caution to a more aggressive stance. Some say the era of 'bide your time' has ended. In its more assertive, redefined place in the world, China has put the South China Sea into its 'core national interests' category of non-negotiable territorial claims - the same league as Taiwan and Tibet . In reaction, US Secretary of State Hillary Rodham Clinton issued a challenge to Beijing at the Asean forum, saying Washington had 'a national interest' in the South China Sea. While no Chinese official has spoken about what 'core national interests' means, there is a growing chorus from within the country for the People's Liberation Army to defend these core interests in the disputed region. Recent news coverage has brought the term 'core national interests' into the same spotlight as 'national sovereignty' and 'territorial integrity' and raises the issue of how China defines the term and what it covers. Professor David Shambaugh, director of the China Policy Programme at George Washington University, said Beijing had long used the term when discussing Tibet and Taiwan to signify issues that go to the heart of its national sovereignty. 'Actually, the Chinese government first applied the term 'core national interest' to the South China Sea in March during the Beijing visit of Deputy Secretary of State James Steinberg and the National Security Council's Asia director, Jeffrey Bader,' Shambaugh said. China has long observed a policy of putting aside disputes over territorial waters with neighbouring countries and jointly developing their natural resources. Analysts said China was now pushing to extend its jurisdiction out to sea as far as possible. Shambaugh said the specific objectives of the new assertion are confined to China's sovereign claim over territories. 'As far as I am aware, there are now four such 'core national interests' that the Chinese government has defined: Taiwan, Tibet, Xinjiang and the South China Sea,' Shambaugh said. 'What they all have in common is that they are territorial parts of the People's Republic of China, to which either other countries or political entities lay competing claims and/or where there are active secessionist movements.' Shambaugh said that, 'having defined these territories as such [a core national interest], China will brook no foreign interference or contesting of its sovereign claim to these territories'. Dr Steve Tsang, a China analyst and professorial fellow at Oxford University's St Antony's College, said core national interest was a key term in Chinese policy. 'When something is elevated to this status, Beijing holds the line firmly over its core national interests, and expects other nations to respect that - as in the cases of Tibet and Taiwan,' Tsang said. Why does China do this? Rear Admiral Zhang Huachen , deputy commander of the PLA's East Sea Fleet, said: 'With the expansion of the country's economic interests, the navy wants to better protect the country's transport routes and the safety of our major sea lanes.' Xu Guangyu, a retired general, said: 'We kept silent about territorial disputes with our neighbours in the past because our navy was incapable of defending our economic zones, but now the navy is able to carry out its task.' For the outside world, the more worrisome issue is what will happen next. Questions have been frequently raised recently about whether Beijing is using the term more often and expanding it to cover other controversial areas such as human rights, the yuan's foreign exchange rate and issues concerning the communist state's national economic safety. An unconfirmed report recently suggested that State Counsellor Dai Bingguo had recently defined 'core national interests' as 'upholding the basic system and national security, defending sovereignty and territorial integrity and safeguarding sustainable economic and social development'. But some mainland academics dismissed the report and any fears that China would expand its definition to cover broader issues, saying that 'core national interests' would be confined to sovereignty and territorial integrity. 'There is consensus within Chinese diplomatic circles and think-tank scholars that the term will apply to only two categories - territorial integrity and sovereignty - at least for the moment,' said Professor Jin Canrong, associate dean of Renmin University's School of International Relations. In an article published in the official Outlook magazine last week, National Defence University professor Han Xudong cautioned that it would be inadvisable for China to make public what its 'core national interests' would cover. 'To publicise what China's core national interests cover is counterproductive to the country's effort to preserve [them],' Han said. The country simply does not have the military or national strength to defend its core interests, Han said, and as such should not publicise its policy. Han noted that even the United States and Russia - which have the world's two most powerful military forces - have not made public what their core national interests cover. Washington has identified its 16 strategically most significant marine lanes as 'important interests', second to its 'vitally important interests', Han said. 'Under such circumstances, our country must preserve our [other] 'national interests', not just 'core national interests',' Han said. Han also warned that overemphasis on 'core interests' would create the illusion that China cares only about its 'core interests' at the expense of 'non-core interests'. 'We should not use the term 'core national interest' to cover all national interests, as it will affect our efforts to preserve all those national interests,' Han said. Tsang, of Oxford, warned the increasingly assertive approach of declaring core national interests would trigger negative reactions. 'The downside of this approach is ... that it will cause strong negative reactions from the region and will harm the peaceful-rise policy,' he said. Han also warned of the possibility of military conflict because of China's redefined stance. 'It could leave either side in dire straits ... with a great possibility of having to resolve the dispute through military means, as both claim that is their own 'core interest',' Han wrote. But Tsang still sees flexibility for Beijing and cites Taiwan as a clear example. 'If its claim is not challenged over a period of time, its claim gets de facto international acceptance - as in the cases of Tibet and Taiwan,' he said. Perhaps the most immediate danger arises from the fact that both China and the US have claimed the region to be in their core national interest and no military crisis-management system exists between the two powers. Beijing suspended military contacts when the US said in January that it would sell defensive arms to Taiwan. Among the activities frozen were the bilateral Military Maritime Consultative Agreement, set up to promote a common understanding in conducting naval and air operations in line with international law. Professor Shi Yinhong, an international security expert at Renmin University, said that now that both countries had listed a disputed territory as their own core national interest, it would be difficult for either side to back down. A key underlying problem for Beijing to expand its core national interests to cover its disputed territory with neighbouring nations and the nearby waters is that China and the US-led West have sharply divergent views of free navigation - not only by civilian ships, but also the rights of foreign military ships and aircraft in waters and airspace. Tsang said the contrast with Latin America under the Monroe Doctrine of the 19th century is that most of the great powers of the time did not have vital interests in that part of the world, and they, being European powers with limited means to project power so far away, did not see a need to challenge the US assertion. 'China may be the biggest regional power, but it's not the only great power,' Tsang said. 'In a situation like this, China is well advised to bear in mind ... the reality that an action will lead to a reaction or, in the case of international politics, even multiple reactions,' he said. But Jin of Renmin University said history had shown that any rising power would advance its own national interests in line with its rising clout, and China was a case in point. 'The world should also be advised to get used to China's rising profile on the global stage,' he said. 'The country has got richer and more developed - though it is too early to say whether Beijing will stop biding its time and will act to assert itself.'