In a move that could soon bring Boston’s Olympic aspirations to an end, Mayor Marty Walsh said Monday he would refuse to sign a contract for the games that would require taxpayers to pay for cost overruns.

“I cannot commit to putting taxpayers at risk,” Walsh said at an unscheduled morning press conference. “If committing to signing a guarantee today is what’s required to move forward, then Boston is no longer pursuing the 2024 Olympic and Paralympic games.”

The declaration comes as the United States Olympic Committee has apparently been pressuring the city to formalize commitments for the 2024 Olympic Games, for which there is a September deadline.

Walsh said he wants to learn more about the cost of the games, and has urged Olympic organizers to provide insurance coverage that would protect the state. He said he has not seen enough information to be confident in the bid.

“I refuse to mortgage the future of the city away,” Walsh said.

The USOC was also set to meet Monday morning, a meeting that would include Massachusetts Gov. Charlie Baker.

Walsh was also drawing criticism online today after he said in an unscripted remark that critics of the Olympics were “about ten people on Twitter.” #10PeopleOnTwitter is now trending in Boston.