A new Pentagon report says China has reclaimed more than 3,200 acres of land in the south-eastern South China Sea. But the country’s focus has shifted to developing and weaponizing those man-made islands so it will have greater control over the maritime region without resorting to armed conflict.

In its most detailed assessment to date of China’s island-building program, the defense department said three of the land features in the Spratly Islands now have nearly 10,000ft runways and large ports in various stages of construction.

And it has excavated deep channels, created and dredged harbors, and constructed communications, logistics and intelligence gathering facilities.

The report argues that the accelerated building effort doesn’t give China any new territorial rights. But it says the airfields, ship facilities, surveillance and weapons equipment will allow China to significantly enhance its long-term presence in the South China Sea.

“This would improve China’s ability to detect and challenge activities by rival claimants or third parties, widen the range of capabilities available to China, and reduce the time required to deploy them,” according to the report released on Friday.

“China is using coercive tactics short of armed conflict, such as the use of law enforcement vessels to enforce maritime claims, to advance their interests in ways that are calculated to fall below the threshold of provoking conflict,” the report adds.

The 3,200 acres only represents China’s reclamation in the Spratleys and doesn’t include its building in the Paracels, further northwest, including the contested Woody Island, in its estimates. China has deployed anti-aircraft missiles to Woody Island.

Chinese officials have defended the land reclamation by saying it is Beijing’s territory, adding that the buildings and infrastructure are for public service use and to support fishermen. It accuses the Philippines, Vietnam and others of carrying out their own building work on other islands.

The report also notes that China has continued to assert sovereignty over the East China Sea, including the Senkaku Islands, which are administered by Japan.

Vietnam, China and Taiwan all claim the Paracels, and the three along with the Philippines, Malaysia and Brunei claim all or parts of the Spratlys. The US says it takes no side in the territorial disputes, but supports freedom of passage through the area, which is one of the world’s busiest sea lanes.

China’s island building, the report concludes, is designed to walk right up to – but not cross – “the threshold of provoking the United States, its allies and partners, or others in the Asia-Pacific region into open conflict”.

More broadly, the report says that China is steadily increasing its role and power around the world, while continuing to modernize and build up its military and inventory of ships, missiles and aircraft.

Specifically, it notes China’s plans to build its first overseas military facility in Djibouti to help support naval operations in the region.

The report also repeats assertions by Defense Secretary Ash Carter that continued provocation by China may only improve US relations in the Asia Pacific.

“China’s increasingly assertive efforts to advance its national sovereignty and territorial claims, its forceful rhetoric, and lack of transparency about its growing military capabilities and strategic decision-making continue to raise tensions and have caused countries in the region to enhance their ties to the United States,” the report said.

US officials have been increasingly concerned China’s activities could be a prelude to enforcing a possible air defense identification zone over the South China Sea, similar to one it declared over disputed Japanese-held islands in the East China Sea in 2013.

As noted in previous year’s reports, China continues to target US government and defense department computer systems through cyber intrusions. The report said that during 2015, China used its cyber capabilities to spy on the US and steal information from computer networks.

“The information targeted could potentially be used to benefit China’s defense industry, high-technology industries, and provide the CCP insights into US leadership perspectives on key China issues,” the report said.