Rumours have long swirled about China's desire to use the Ream naval base on Cambodia's stretch of the Gulf of Thailand, giving its ships ready access to the strategically crucial South China Sea.
According to an embassy official in Phnom Penh, Cambodia inexplicably withdrew a request for American help to repair part of the base in Sihanoukville last month.
Instead Cambodia signed a secret 30-year agreement with China, The Wall Street Journal reported on Monday, allowing the regional superpower to post personnel at the base, dock warships, and store weapons there.
Senior Cambodian officials on Thursday repeated premier Hun Sen's denial of the WSJ report as "fake news".
"It is ill-intended news created to incite," General Chhum Socheat told reporters.
"We have never had any secret military deal," he added.
"Cambodia does not need the presence of any foreign soldiers," added An Sokhoeun from the foreign affairs ministry.
The country's constitution prevents a foreign military presence on Cambodian soil.
But Chinese influence inside the kingdom has deepened in recent years with the building of casinos, condos and roads as well as with billions of dollars of loans to the government.
The relationship has tilted the balance away from the US, which has been edged out since Hun Sen -- who has been in power for more than three decades -- breezed to victory in elections held last year without an opposition.
But analysts say Hun Sen is concerned about an anti-China backlash from the public, especially in Sihanoukville where many businesses are Chinese-owned.
Tensions simmered in the southwestern city last month when an under-construction Chinese building collapsed killing 28 people.
The US Embassy official said the sudden withdrawal of the request for help to repair the Ream base had raised suspicions of a wider motive.
"This causes us to wonder if the Cambodian leaderships' plans for Ream Naval Base include the possible hosting of foreign military assets and personnel on Cambodian soil," the official told AFP.
"We are concerned that a possible Chinese military presence in Cambodia would both threaten regional stability and the position of ASEAN."