The report said that while the PLA had continued to extend operations, it was not clear what message Beijing was seeking to send by carrying out the flights "beyond a demonstration of improved capabilities". Starting with the USA, which objects to its growing trade deficit with China, both sides have announced tariffs on a range of each others' goods.
While Washington and Beijing maintain a military-to-military relationship aimed at containing tensions, this has been tested in recent months, notably in May when the Pentagon withdrew an invitation to China to join a multinational naval exercise.
"The PLA continues to strengthen its military space capabilities despite its public stance against the militarisation of space", it said.
China also continues to develop counterspace capabilities, "including kinetic-kill missiles, ground-based lasers and orbiting space robots", the report said, a time when US President Donald Trump plans to establish a Space Force by 2020 to protect US assets in space.
Long-range bomber training missions "targeting the US" - this is how the United States mainstream media reported the findings of the Pentagon's annual assessment of Chinese military capabilities in 2017, published Thursday.
The US military regularly seeks to demonstrate freedom of navigation by flying over the South China Sea.
China is engaged in a decades-long build-up and modernisation of its once-backward armed forces, and military leaders have set a goal of fielding a world-class military by 2050.
The report highlights its increasing military capability, including defence spending estimated at $190bn (£150bn) - a third that of the US.
The South China Morning Post says Chinese president Xi Jinping "ordered the PLA to step up efforts, saying China needed a military ready to "fight and win" wars".
The call has alarmed China's neighbours, several of whom are embroiled in tense border disputes with the superpower.
The report also found that China is advancing "an ambitious agenda of military modernization and organizational reforms".
The Pentagon report said that despite a projected slowdown in economic growth, China's official defence budget would be more than $240bn by 2028.
The document warns that China "is likely preparing for a contingency to unify Taiwan with China by force".
"Should the United States intervene, China would try to delay effective intervention and seek victory in a high-intensity, limited war of short duration", the report warns.
An article published by the Sina military channel yesterday said that the artillery deployed in the drills were PLL-09, a Chinese 122-millimeter self-propelled howitzer. A "stealthy, long-range strategic bomber with a nuclear delivery capability" could be operation "within the next 10 years", the report says, completing the so-called "nuclear triad" of delivery systems.