"While we value our long friendship with the Thai people, this act will have negative implications for the U.S.-Thai relationship, especially for our relationship with the Thai military," Xinhua quoted Kerry as saying Thursday in a statement.
The top US diplomat said he was "disappointed" by the decision of the Thai military to suspend the constitution and take control of the government after a long period of political turmoil.
There was "no justification" for the military coup, Kerry said, calling for the release of senior political leaders of major parties in Thailand, a treaty ally with the United States.
"I urge the restoration of civilian government immediately, a return to democracy, and respect for human rights and fundamental freedoms, such as press freedoms," he said.
State Department spokeswoman Jen Psaki said up to $10 million, the annual amount of US bilateral assistance to Thailand, could be suspended.
"We've taken preliminary steps to suspend military engagement and assistance while we consider the facts on the ground," Psaki told a regular briefing.