Australia has signed a treaty with the Pacific island nation of Nauru to provide aid, banking and other infrastructure support, the latest maneuvering for influence in the region between China and countries allied with the United States.

In a clear nod to China, the five-year deal, announced on Monday, mandates that Nauru will consult Australia when entering partnerships or agreements in vital sectors including telecommunications, banking or cybersecurity. The two countries agreed that “a third party” may not co-opt Nauru’s critical infrastructure for security purposes.

In exchange, Australia will provide the country with 140 million Australian dollars (about $90 million) over the five years in budget support and security assistance, a substantial sum for Nauru, a tiny island of 13,000 people and a $150 million economy.

“It is about containing Chinese influence,” said Meg Keen, a senior fellow in the Pacific Islands Program at the Sydney-based Lowy Institute. “This deal effectively can lock out China from engagement in the security sector, in particular policing and military.”

Australian and American officials were caught off guard in 2022 when China announced a sweeping security pact with the Solomon Islands that opened the door to a Chinese military presence on the archipelago. The Solomon Islands lie about 1,200 miles to Australia’s northeast, halfway to Nauru.

That agreement put the United States and the region on edge amid signs in recent years that China was seeking to expand its reach in the Pacific, offering policing and security assistance and developmental aid.