A proposed Olympic Stadium in Boston. (Boston2024 / Handout via Reuters)

The United States Olympic Committee declared an end to Boston’s bid to host the 2024 Games after the city’s mayor said he could not commit to the bid, refusing to sign the host city document.

Mayor Marty Walsh said at a hastily-called Monday morning press conference timed to coincide with Gov. Charlie Baker’s meeting with the USOC, that he would prefer not to host the Games if it meant that city taxpayers would have to foot the bill for cost overruns. The contract must be signed before a city can officially be chosen as host and Walsh wouldn’t budge.

“If committing to signing a guarantee today is what’s required to move forward” Walsh said (via the Boston Globe), “then Boston is no longer pursuing” the Games.

By early afternoon, an unnamed official told the Globe: “It’s over.”

In a statement, Scott Blackmun, the USOC chief executive, noted that “we have not been able to get a majority of the citizens of Boston to support hosting the 2024 Olympic and Paralympic Games. Therefore, the USOC does not think that the level of support enjoyed by Boston’s bid would allow it to prevail over great bids from Paris, Rome, Hamburg, Budapest or Toronto.”

Boston’s bid was in trouble shortly after it began in January because of low public support and active opponents, although Walsh declared them to be “10 people on Twitter.” At the Monday press conference, the Globe reports that:

Walsh said that he would not “mortgage the future of the city away” until he learned more about the exact wording of that cost overrun guarantee. However, that guarantee won’t be fully released until September. Walsh said his Office of Olympic Planning is unable to do an analysis of the bid’s potential costs without that full information.

“I think it’s unfortunate that it’s come to this point,” he said. “I’m not signing the agreement that’s going to cost the taxpayers to pony up if there’s overruns.”

The deadline to officially nominate a city is Sept. 15 and, if the USOC intends to submit a bid, Los Angeles is the next likely choice, the Associated Press reports. Boston was chosen over Washington, San Francisco and L.A.