A US think tank says two Chinese warships are anchored at a Cambodian port seen as having key strategic value.

Ream Naval Base is undergoing expansion, with financial help from China. Washington suspects Beijing is using it for military purposes. Cambodia says that's not the case.

The Center for Strategic and International Studies reported on Thursday that two Chinese navy ships have spent over four months at the base.

It says the ships are the only ones to have docked at a new pier built there with Chinese funding.

Last year, Cambodia's defense minister posted photos of a visit he made to the base. Vessels believed to be Chinese warships were visible in them.

The naval base in southern Cambodia is located near the South China Sea, where Beijing and Southeast Asian nations have territorial disputes.

The Wall Street Journal reported in 2019 that Cambodia secretly concluded an agreement allowing China's military to use the base in return for the assistance.

Washington expressed "serious concerns" about Beijing's plans for exclusive control over parts of the base.

Phnom Penh denies China's military is using the port. Earlier this month, former Prime Minister Hun Sen -- now president of the Senate -- suggested on Facebook that Cambodia would be violating its own Constitution and independence if it let the Chinese military into the country. He added, "We call on you not to slander us in order to oppose China."