In what experts say may signal plans to significantly expand its nuclear capabilities, China has begun constructing more than 100 new missile silos in a desert area in the western part of the country, according to a report.

Work at 119 sites was clearly visible and resembled existing missile-launch facilities, according to satellite images obtained by the James Martin Center for Nonproliferation Studies in Monterey, California, The Washington Post reported Wednesday.

The sites were not the only areas in China where launch facilities were under construction, one nuclear watcher told the newspaper.

"If the silos under construction at other sites across China are added to the count, the total comes to about 145 silos under construction," said Jeffery Lewis, director of the East Asia Nonproliferation Program at the Center for Nonproliferation Studies, according to the Post.

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"We believe China is expanding its nuclear forces in part to maintain a deterrent that can survive a U.S. first strike in sufficient numbers to defeat U.S. missile defenses," he added.

"We believe China is expanding its nuclear forces in part to maintain a deterrent that can survive a U.S. first strike in sufficient numbers to defeat U.S. missile defenses."

— Jeffery Lewis, Center for Nonproliferation Studies

The work in China signals possible intentions to upgrade the country’s nuclear arsenal from the existing 250 to 350 weapons – a more modest total when compared to the U.S. and Russia, the Post reported.

The U.S. is believed to have a total of more than 5,500 nuclear warheads, including around 1,700 that have been retired and are awaiting dismantlement, according to the website of the Center for Arms Control and Non-Proliferation.

Russia is believed to own more than 6,200 warheads, including those slated for retirement, according to the website of the Federation of American Scientists.

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Other nations in the so-called "nuclear club" include France, Britain, Pakistan, Israel and North Korea, each with far smaller totals of warheads, according to the site.

The report of China’s new silo construction follows recent warnings by Pentagon officials about the nation’s nuclear expansion plans, the Post reported.

In February, Chinese officials dismissed U.S. worries about its potential new nuclear ambitions as "groundless" and a "vilification" of the country.

"There is an order-of-magnitude difference between the amount of China's nuclear weaponry and that of the United States and Russia," Chinese Ministry of Foreign Affairs spokesman Wang Wenbin told reporters Feb. 5. "We firmly reject the groundless allegation and vilification from the U.S. side."

Nevertheless, in April, Adm. Charles Richard, commander of U.S. Strategic Command, urged lawmakers on Capitol Hill to support an upgrading of the U.S. nuclear arsenal, warning of recent investments by Russia and China.

"I cannot deter with the leftovers from the Cold War forever in the future," Richard told members of the Senate Armed Services Committee.

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He referred to the U.S. arsenal as a "70s-era weapons system that I am going to have to employ against 2030-level threats" if lawmakers fail to support improvements.

In early June, top House Republicans urged President Biden to create a strategy for combatting a Chinese nuclear build-up.

In a letter to the president, U.S. Reps. Mike Rogers, Mike McCaul and Devin Nunes pointed to Adm. Richard’s Capitol Hill testimony, warning Biden that China has "moved a portion of its nuclear force to a Launch on Warning posture and has a nuclear weapons stockpile that is expected to at least double, if not triple, or quadruple, over the next decade." 

Fox News’ Caitlin McFall, Lucas Y. Tomlinson and Brooke Singman contributed to this story.