Cambodia has pledged to spend an additional $40 million on Chinese weapons to modernise its military, in a move that is likely to compound US fears about Phnom Penh’s growing proximity to Beijing as China spreads it influence across Southeast Asia.

Cambodia’s military ties with ally China have been under particular scrutiny over reports that a secret deal has been signed to allow Chinese forces to use a Cambodian naval base to dock warships and store weapons.

The Wall Street Journal last week alleged the existence of a draft deal allowing China to access Ream base near Sihanoukville, which would give Beijing a strategic advantage in the Gulf of Thailand and ready access to the disputed South China Sea.

Cambodia has denied the reports and Hun Sen, the prime minister, called the news “slander.”

However, Cambodia, which has faced sharp criticism from Western nations over its shrinking political freedoms has grown increasingly closer to China in recent years, with ties boosted by billions of Chinese-funded soft loans, and investment in Cambodian infrastructure projects.

On Monday, the prime minister revealed during a trip to a Chinese-financed stadium in Phnom Penh that he had ordered the purchase of “tens of thousands of additional weapons," from Beijing. He did not disclose what the armory was but said it was already being shipped.