After Chinese state media warned that war with the United States may be “inevitable,” Beijing has published a policy paper detailing how the military will shift its focus from land and coastlines to the open seas. China’s State Council released a white paper today that criticizes “external countries…busy meddling in South China Sea affairs” and sets out an “active defense” military strategy for the country.

The paper comes a day after an editorial (link in Chinese) in the state-run Chinese tabloid Global Times said conflict between China and the US will be unavoidable if the Washington doesn’t lay off Beijing for building islands and military facilities in disputed parts of the South China Sea.

“We do not want a military conflict with the United States, but if it were to come we have to accept it,” the paper said. (Editorials in state-run papers are not official representations of Beijing’s position, but often reflect government sentiment.)

The US has been calling on China to halt the construction of entire islands with ports, army barracks and at least one air strip near the Spratly Islands. The area—one of the world’s busiest shipping lanes and home to fertile fishing grounds as well as possibly oil and gas—is the focus of overlapping claims by China, the Philippines, Malaysia, Vietnam, Taiwan, and Brunei.

According to the white paper, the People’s Liberation Army Navy will expand its defense perimeter to include “open seas protection.” The air force will also expand its focus to include offensive as well as defensive military capabilities. “We will not attack unless we are attacked, but we will surely counterattack if attacked,” the paper said.

Chinese authorities denied the white paper had anything to do with tension over US surveillance of China’s building in the Spratlys. On Monday, China’s foreign ministry said that it had filed a complaint with the US for flying a spy plane near Chinese island construction sites last week.

International security experts have long said that armed conflict between the two countries is unlikely given their economic reliance on each other. Increasingly scholars and analysts say that war may not be “as improbable as many experts suggest” because of growing dominance of hardliners in the Chinese government, increased rivalry, or general lack of trust between the countries.

The US and other states are preparing for any potential confrontation. Southeast Asian countries are building up their navies and coastguards—defense spending in the region is expected to reach $52 billion by 2020, up from a projected $42 billion this year, IHS Janes Defence has said.

Last week, US vice president Joe Biden told graduates at the Naval Academy in Annapolis that 60% of the United States Naval force will be stationed in the Asia Pacific by 2020, in order to stand up for freedom of navigation and peaceful, equitable resolution to territorial disputes. “Today, these principles are being tested by Chinese activities in the South China Sea…We are going to look to you to uphold these principles wherever they are challenged,” he said.