China's military conducted cyber probes and intrusions against U.S. computer networks to support intelligence collection and electronic warfare even as it continues an "extraordinarily rapid" expansion of long-range precision strike capabilities, according to a new Pentagon report.

"China is using its cyber capabilities to support intelligence collection against the U.S. diplomatic, economic, and defense industrial base sectors that support U.S. national defense programs," the Defense Department said in its annual report on China's capabilities, published Friday.

The report, which traditionally draws a strong reaction from the Chinese government, comes ahead of a visit to Vietnam and Japan this month by President Barack Obama and amid increasing tensions between the United States, China and Southeast Asian nations over sovereignty claims in the South China Sea.

Highlighting what the Pentagon described as China's focus on improving cyber capabilities to counter a "stronger foe," the report said information gleaned by hackers "could inform Chinese military planners' work to build a picture of U.S. defense networks, logistics, and related military capabilities that could be exploited during a crisis."

"The accesses and skills required for these intrusions are similar to those necessary to conduct cyber attacks," according to the report. The intelligence gathering could also provide the ruling Communist Party "insights into U.S. leadership perspectives on key China issues."

In the South China Sea, President Xi Jinping's military last year "accelerated land reclamation and infrastructure construction at its outposts in the Spratly Islands," which when complete "will include harbors, communications and surveillance systems, logistics facilities, and three airfields."

"Although artificial islands do not provide China with any additional territorial or maritime rights within the South China Sea, China will be able to use its reclaimed features as persistent civil-military bases to enhance its presence in the South China Sea significantly and enhance China's ability to control the features and nearby maritime space," it said.

At least six nations, including China, Vietnam and the Philippines, have competing sovereignty claims in the South China Sea.

Adding to tensions, Chinese naval vessels followed and sent warnings to the USS William P. Lawrence this week as the vessel sailed within the 12-nautical-mile territorial zone around Fiery Cross Reef, a feature in the Spratly Islands where China has dumped hundreds of thousands of tons of sand and coral to create an island on which it has built an airstrip.

China called the U.S. warship's maneuvers "a naked challenge." The U.S. said it was a "freedom of navigation" operation in international waters, one of many it has taken near contested reefs and outcrops.

While China has a no-first-use policy toward nuclear weapons, the report also suggests -- based on Chinese media reports and military writings -- that the country intends to build a stealth bomber to carry nuclear weapons.

"If it does, China would develop a 'triad' of nuclear delivery systems dispersed across land, sea and air -- a posture considered since the Cold War to improve survivability and strategic deterrence," according to the report. The U.S. has plans to modernize its long-standing nuclear triad.

