China possessed "more than 500 operational nuclear warheads as of May 2023 -- on track to exceed previous expectations" the Department of Defense said in its annual China Military Power Report, issued annually and mandated by Congress.

"We're not trying to suggest a very large departure from where they looked to be headed... but we are suggesting that they're on track to exceed those previous projections," a senior defense official told journalists.

Nevertheless, the uptick "raises a lot of concerns for us," the official said, speaking on the condition of anonymity.

Beijing is likely to have more than 1,000 operational nuclear warheads by 2030, the report added.

The United States currently possesses about 3,700 nuclear warheads, trailing Russia's roughly 4,500, according to the Stockholm International Peace Research Institute, which counts 410 warheads for China.

The report also detailed an expanding and modernizing Chinese military, in line with China's more assertive role on the world stage under President Xi Jinping.

Earlier this week the United States accused China of orchestrating a "concerted" campaign of dangerous and provocative air force maneuvers against US military planes in international airspace, warning such moves could spark inadvertent conflict between the two powers.

The Pentagon said aggressive tactics by Chinese aircraft threatened US planes flying over the East and South China Sea regions, tallying more than 180 such incidents since fall 2021 -- "more in the past two years than in the decade before that," Ely Ratner, assistant secretary of defense for Indo-Pacific security affairs, told reporters Tuesday.

Ratner alleged there was an intentional campaign by Beijing "to perform these risky behaviors in order to coerce a change in lawful US operational activity."

US-China relations are at their lowest point in years, with tension over a range of issues including trade, human rights, Taiwan and the South China Sea.

The Defense Department official speaking about the nuclear report urged China "to be more transparent on their nuclear buildup," though Beijing doesn't communicate with Washington on its arsenal.

The report noted that China is looking to expand its capacity to launch its warheads -- via land, air and submarine -- and has "probably completed" the construction of a total of 300 intercontinental ballistic missile launch facilities.

While the United States says it now sees China as its top geopolitical rival, China has pushed back over what it calls a US policy of containment and encirclement against it in the Pacific and elsewhere.

Amid the historic tensions, the two countries have renewed dialogue with a succession of visits by senior US officials to Beijing in recent months, but Ratner on Tuesday said that Beijing continues to decline US invitations "to open lines of military-to-military communication at the senior-most levels."