For the first time China is close to reaching a "credible" nuclear deterrent based on land-based, submarine-launched and air-dropped nuclear weapons, a draft US report warned Friday.

The report by the US-China Economic and Security Review Commission said China's military, the People's Liberation Army, "continues to modernize and expand its nuclear stockpile."

"China is now on the cusp of attaining a credible nuclear triad of land-based intercontinental ballistic missiles, submarine-launched ballistic missiles, and air-dropped nuclear bombs."

AFP obtained a draft of the annual report, scheduled to be delivered to the US Congress on Wednesday.

China has had "a symbolic ballistic missile submarine capability" for decades, based on a single aging submarine, but it is now close to having its first "credible, near-continuous at-sea strategic deterrent," the report said.

Two JIN-class submarines capable of launching missiles have already been deployed and three more are planned.

They will be equipped with JL-2 intercontinental ballistic missiles -- a program still in development that "may reach initial operating capability within the next two years," the report said, quoting the US Department of Defense.

China has been a nuclear power since 1964, and the country currently has between 50 and 75 land-based intercontinental ballistic missiles.

China also has some 20 long-distance aircraft able to deliver nuclear bombs, according to the Federation of American Scientists (FAS), also cited in the report.

The report cautioned that the Asian giant "has disclosed little information about the size, composition, and disposition of its nuclear forces, which yields uncertainties about the size and characteristics of its warhead inventory."

"Outside assessments from western observers, which generally range from about 100 to 500 warheads, but cluster around 240, rely heavily upon assumption," the report said.

Likewise, China's process of authorizing the use of a nuclear weapon also remains obscure.

"Questions remain about whether China has a 'two-man rule' or other provisions in place to ensure that, with emerging mobile platforms, launches can take place only with authorization," the report said.

Also worrisome to US officials is the relationship between China's civilians and their military.

"What worries me most are the disconnects that tend to occur between (China's) government and their military," said former US Joint Chiefs of Staff vice chairman James Cartwright in testimony to the commission.

The report pointed to China's 2007 anti-satellite demonstration, and the 2011 test flight of its J-20 fighter aircraft that took place as US Secretary of Defense Robert Gates was visiting China, "both of which may have caught China's civilian leadership off guard."