US-China war 'inevitable' unless Washington drops demands over South China Sea

China has vowed to step up its presence in the South China Sea in a provocative new military white paper, amid warnings that a US -China war is "inevitable" unless Washington drops its objections to Beijing's activities.

In the new policy document published on Tuesday, China outlined its plans to shift from a defensive military posture to placing emphasis on offensive capabilities.

Claiming that it faces a "grave and complex array of security threats", including challenges to its sovereignty over the South China Sea, the policy document released by the State Council says the military will step up its "open seas protection".

China's forces will no longer be limited to defence of the nation's territory but will project its military power further beyond its borders at sea and more assertively in the air in order to safeguard its maritime possessions, the white paper states.

While the air force will shift focus from "territorial air defence" to both offence and defence, the Chinese army will increase its global mobility and its artillery will improve its "medium and long-range precision strikes", it said.

In an editorial in The Global Times, a tabloid owned by the Chinese Communist Party through another newspaper, the paper described the construction of runways, harbour facilities and buildings on the disputed Spratly Islands as the nation's "most important bottom line".

The article – which appeared just days after a US aircraft ignored repeated warnings from the Chinese military to fly a reconnaissance mission over the islands – said Beijing does not want a conflict with the US, "but if it were to come, we have to accept it.

"If the United States' bottom line is that China has to halt its activities, then a US-China war is inevitable in the South China Sea", said the paper, which is often seen as a mouthpiece of the government in Beijing.

Xinhua News Agency also reported on Tuesday that work has begun on two lighthouses on reefs in the South China Sea that are claimed by Vietnam and the Philippines.

Speaking at a press conference in Beijing, Yang Yujun, a spokesman for the defence ministry, dismissed international criticism of China's policies in the South China Sea, claiming development work is the same as building roads and homes on mainland China and that it would benefit "the whole of international society".

"From the perspective of sovereignty, there is absolutely no difference", he said, adding that "some external countries are also busy meddling in South China Sea affairs".

Analysts say neither Washington nor Beijing appear to be in the mood to back down and that there is a serious risk of a minor incident in airspace around the islands escalating rapidly.

"I think the concern has to be that China misjudges the situation", said Robert Dujarric, director of the Institute of Contemporary Asian Studies at the Japan campus of Temple University.

"Neither party wants a war if it can be avoided, but there are red lines for both sides", he said. "I worry that if Beijing considers the US to be a declining power and assumes that Washington will back down if it shoots down a US observation aircraft".

And while Washington chose to "de-escalate" the crisis after a Chinese fighter collided with a US Navy intelligence-gathering aircraft off Hainan Island in April 2011, Prof. Dujarric says he would expect a different response if a similar incident were to occur in what Washington insists is international air space over the South China Sea.

Recent developments have provoked new concerns in the region, with Ma Ying-jeou, the president of Taiwan, calling for the different nations laying claim to the South China Sea to put their differences aside and carry out joint development of natural resources.