Washington has said the Ream naval base, located off Cambodia's southern coast, could give Beijing a key strategic position in the Gulf of Thailand near the disputed South China Sea, which China claims almost in its entirety.

"The first phase of the Ream base is planned to be inaugurated on April 2," Major General Thong Solimo, spokesman for the Royal Cambodian Armed Forces (RCAF), told AFP.

RCAF's Commander-in-chief Vong Pisen told Japanese military attache officials about the schedule during a meeting on Tuesday, Thong Solimo said, adding that Cambodia would "allow a Japanese military ship to dock at the Ream base first" following the ribbon-cutting.

General Chhum Socheat, a defence ministry spokesman, told AFP that ships from "friends of Cambodia" would also be allowed to dock at Ream as long as they met conditions, adding he "did not deny" that would include a US vessel.

Cambodia has long been one of China's staunchest allies in Southeast Asia, and Beijing has extended its influence over Phnom Penh in recent years.

Under former leader Hun Sen -- Prime Minister Hun Manet's father -- China has poured billions of dollars into infrastructure investment, while Washington's relationship with Phnom Penh has deteriorated.

Since 2022, China has been funding the renovation of the Ream naval base which was originally built partly using US funds.

Chinese warships first docked at the 363-metre (1,190-foot) pier in December 2023.

In December 2024, a US warship docked in Cambodia in the first American military port call in eight years.

A senior US army commander visited Cambodia in February and met with Hun Manet to "expand bilateral defence ties".

Cambodia is set to receive two warships from China to improve its defence capabilities.

Cambodian leaders have repeatedly denied that the base is for use by any foreign power.