China is rapidly expanding infrastructure tied to its nuclear weapons program, with satellite images revealing major construction at seven sites as Beijing faces growing scrutiny over its expanding arsenal.

An investigation published Wednesday identified activity at Pingtong, Zitong, Lop Nur, Jiuquan, Mianyang, Jinta and Guangyuan. The satellite imagery documents substantial construction, although the images alone cannot establish precisely what work is occurring inside the facilities.

At one location, villages and farms reportedly were cleared for a fusion research center where powerful lasers can help scientists study how materials behave under conditions associated with nuclear detonations.

The expansion comes amid a dispute between Washington and Beijing over nuclear testing. U.S. officials have accused China of conducting a secret nuclear test at Lop Nur in 2020 and concealing its activities. China denies the allegation. Available seismic data have not conclusively established that a nuclear explosion occurred.

U.S. Under Secretary of State for Arms Control and International Security Thomas DiNanno has accused China of using techniques designed to make nuclear testing more difficult to detect.

Beijing, meanwhile, maintains a no-first-use nuclear policy and describes its nuclear posture as defensive. Chinese officials have rejected U.S. accusations about a growing nuclear threat and argued that the country's smaller arsenal makes trilateral arms negotiations with Washington and Moscow inappropriate.

The construction adds another national security issue to President Donald Trump's Thursday meeting with Chinese President Xi Jinping in Washington. Artificial intelligence and its growing military implications are also expected to be discussed.

The nuclear question has taken on greater significance following the expiration of the New START Treaty in February. U.S. officials have argued that an arms-control framework focused only on Washington and Moscow no longer reflects a world in which China is substantially expanding its nuclear capabilities.