A senior US military general has warned during a visit to Australia that China’s offer to deepen security ties with Solomon Islands will come with strings attached, suggesting the Pacific island country may come to regret the planned deal.

“My parents told me if a deal sounds too good to be true, it probably is,” the commandant of the United States Marine Corps, general David Berger, said on Wednesday.

Berger was cautious when asked about longstanding US concerns relating to a Chinese company’s lease over the port of Darwin, stressing it was a sovereign decision for Australia as part of its yet-to-be-completed national security review.

Ahead of a trip to Darwin, the site of increasing rotations of US Marines, Berger said: “If it’s not of concern to Australia, then it’s not of concern to me.”

Berger’s visit comes amid a flurry of diplomatic activity by the US and Australia attempting to head off a proposed security agreement between China and Solomon Islands, which could allow regular visits by the People’s Liberation Army Navy.

A leaked draft from last month raised the possibility China could “make ship visits to, carry out logistical replenishment in, and have stopover and transition in Solomon Islands”, while Chinese forces could also be used “to protect the safety of Chinese personnel and major projects in Solomon Islands”.

The prime minister of Solomon Islands, Manasseh Sogavare, has sought to allay concerns, saying his country has no intention of allowing a Chinese naval base. But Sogavare has also said it is “very insulting to be branded as unfit to manage our sovereign affairs”.

Speaking in Canberra on Wednesday, Berger said the US needed to show humility in its outreach to Pacific nations, but also needed to be open about the potential long-term consequences.

Berger reflected on the fight for control of Guadalcanal in Solomon Islands during the second world war, when the US and allies sought to prevent Japanese forces from gaining a foothold in the strategically important location.

“A lot of things change in warfare. Not geography. Where … Solomon Islands are matters. It did then and it does now,” Berger said at the Australian Strategic Policy Institute.

He said the proposed agreement was “just another example” of China seeking to broaden and expand its influence. He raised concerns about “the way that [it] happens and the consequences for the nations” involved.

Sogavare has argued Solomon Islands pursues a “friends to all and enemies to none” foreign policy, but Berger implied countries making agreements with Beijing might regret it down the track.

“We should illuminate, we should draw out into the open what this means long term,” Berger said.

“This is, in other words, an extension of ‘hey we’re here with a cheque, we’re here with money, we’d like to improve your port or your airfield or your bus station’. And that just sounds so great, until a year later or six months later.”