America’s top diplomat expressed concern to Southeast Asian foreign ministers about China’s growing nuclear arsenal, the State Department said Friday.

Secretary of State Antony Blinken outlined to the ASEAN Regional Forum, an online meeting of more than 20 countries, a list of provocative Chinese behavior.

“The secretary also noted deep concern with the rapid growth of the PRC’s nuclear arsenal which highlights how Beijing has sharply deviated from its decades-old nuclear strategy based on minimum deterrence,” State spokesman Ned Price said, referring to the People’s Republic of China.

A report last month from the American Federation of Scientists concluded that Beijing was building more than 100 missile silos in its Xinjiang region, raising questions about China’s nuclear weapons ambitions.

The Stockholm International Peace Research Institute estimates that China holds approximately 350 of the world’s nukes, a fraction of the 5,550 possessed by the United States and 6,255 by Russia.

Blinken also warned about the violent military regime in Burma as well as human rights abuses in Tibet, Hong Kong and Xinjiang.

Last month, the Biden administration warned businesses with ties to Hong Kong and Xinjiang of sweeping regulatory risks as China continues to restrict political and economic freedoms in the region.

Blinken also called on China to cease its provocative behavior in the hotly contested waters of the South China Sea.

The South China Sea, which is home to more than 200 specks of land, serves as a gateway to global sea routes where nearly $4 trillion of trade passes annually. More than $1 trillion of that is linked to the U.S. market. The sea is also home to an estimated $2.6 trillion in recoverable offshore oil and gas.

Five claimants — China, Malaysia, the Philippines, Taiwan and Vietnam — occupy nearly 70 disputed reefs and islets across the South China Sea. Over the years, claimants have built and expanded approximately 90 outposts on these contested features, according to research gathered by CSIS’s Asia Maritime Transparency Initiative.

The numerous overlapping sovereign claims to the land have led to it being a home for military outposts. Beijing holds the lion’s share of these land features, with approximately 27 throughout the area.

Beijing’s interest in developing the land across the South China Sea is by no means new.

China first took possession of Fiery Cross Reef and Subi Reef in 1988 and has since outfitted them with deep-water ports, aircraft hangars, communication facilities, administration offices and a 10,000-foot runway.