A White House statement said Solomon Islands Prime Minister Manasseh Sogavare reiterated to the visiting delegation led by White House Indo-Pacific co-ordinator Kurt Campbell that there would be no military base, no long-term presence and no power projection capability under a security deal signed with China.
The White House gave no indication of what the US response would be to such an eventuality but its blunt tone indicated the level of US concern that led to the dispatch of Campbell's mission to the remote island country this week.
"If steps are taken to establish a de facto permanent military presence, power-projection capabilities, or a military installation, the delegation noted that the United States would then have significant concerns and respond accordingly," it said.
"The United States emphasised that it will follow developments closely in consultation with regional partners."
The statement said the US delegation outlined specific steps it would take to advance the welfare of the people of the Solomons, including by expediting the opening of an embassy there, boosting co-operation on unexploded ordinance and sending the Mercy hospital ship to address health issues.
It said the US would also deliver more vaccines and would advance climate and health initiatives.
It said the two sides had "substantial discussion" on the security agreement with China.
"Solomon Islands representatives indicated that the agreement had solely domestic applications but the US delegation noted there are potential regional security implications of the accord, including for the United States and its allies and partners," the statement said.
The delegation met Sogavare in the Solomons capital Honiara days after the Solomons and China said they had signed a security pact, despite a flurry of calls from the US and its allies urging the island country not to go ahead with a deal they fear will significantly extend China's military reach in the region.
The Solomon Islands occupy a strategic position in the Pacific and were the scene of some of the bloodiest fighting in that theatre of World War II.
On Wednesday, Sogavare, brushing off the international concerns, told parliament the deal would not undermine peace.
Campbell discussed the security agreement with neighbouring Fiji and Papua New Guinea ahead of his visit to Honiara, the US embassy in Papua New Guinea said.
Australian officials said Campbell's visit likely prompted China and the Solomon Islands to announce the agreement was a done deal.
While Sogavare has ruled out hosting a Chinese military base, US allies Australia and New Zealand have expressed concern the pact would disrupt regional security, allowing Chinese naval vessels to replenish in Honiara.
Full details have not been disclosed but the pact will allow Chinese police to protect Chinese-funded infrastructure projects after the country was rocked by riots last year in which four people were killed.
On Friday, Sogavare joined China's ambassador Li Ming at the handover of an athletics field donated by China, one of the sporting facilities worth a total of $US120 million ($A164 million) that China has paid for to help the Solomons host the 2023 Pacific Games.
The Solomons switched diplomatic ties from Taiwan to China in 2019, and Sogavare said in a speech at the ceremony that the decision had "placed the country on the right side of history".
Li defended the security pact.
"Development and security are two sides of a coin. Without safety and security, countries cannot enjoy sustainable development and economic growth. This was demonstrated by the riot last year," he said in a speech.
New Zealand and Tonga have said they will raise the issue at an upcoming meeting of Pacific Islands Forum leaders while Japan plans to send a vice foreign minister to the Solomon Islands this month, the Kyodo news agency reported.
