The US fears that the move will make the facility to transform to host Chinese military assets.

A top Royal Cambodian Navy official told Nikkei Asia on Saturday that the Chinese government was supporting a project to expand the port and develop a ship repair facility at the base on the Gulf of Thailand.

Vann Bunlieng, a three-star vice-admiral, deputy commander and chief of the navy general staff, said the plans include dredging work to deepen the waters surrounding the base, which can currently only accommodate smaller vessels.

"The Chinese government helps us to build a port and repair facility for our ships," Bunlieng  told Nikkei Asia.

Bunlieng told media the new facilities will save Cambodia money on ship repair should it acquire larger vessels.

He said they could also be used to service private vessels to generate revenue. 

Center for Strategic and International Studies  recently unveiled satellite images which showed that a building at the site -- which had been built with U.S funds -- was demolished last month.

"The Cambodian government has demolished a U.S.-built facility at the country’s Ream Naval Base, according to satellite imagery collected on October 1," read the CSIS website.

"The demolition occurred sometime after September 5—likely around September 10—though imagery of sufficient resolution to confirm was not available at that time," it said.

"The building was one of several U.S.-funded facilities on the base which were reportedly to be relocated after Cambodia struck a secret deal to grant China access to Ream," read the website.

"The recent demolition seems to confirm that changes are underway at the naval base and again raises questions about rumored Chinese access," it said.

The building was one of two U.S.-funded facilities at the base cited in a letter from Pentagon official Joseph Felter to Cambodia's Minister of Defense Tea Banh last year, reports Nikkei Asia.

Felther, the U.S. deputy assistant secretary of defense for South and Southeast Asia, had suggested Cambodia's flip-flop on a plan to upgrade the facilities could indicate an intention to host Chinese military assets, the news website reported.

The Wall Street Journal reported in 2019 that China has signed a secret agreement allowing its armed forces to use a Cambodian navy base, as Beijing works to boost its ability to project military power around the globe, according to U.S. and allied officials familiar with the matter.

The pact—signed this spring but not disclosed by either side—gives China exclusive rights to be part of a Cambodian naval installation on the Gulf of Thailand, not far from a large airport now being constructed by a Chinese company, the newspaper reported.

Bunlieng rejected reports that the base would be used by the Chinese military. Both Cambodia's prime minister and Chinese officials have denied the existence of such plans, reports Nikkei Asia.