Boston Mayor Marty Walsh says he would not sign a host-city agreement that included a guarantee that Boston taxpayers would cover cost overruns for a potential 2024 Summer Olympics in Boston.

If the U.S. Olympic Committee wanted Walsh to sign such a guarantee right now, "then Boston is no longer pursuing the 2024 games," Walsh said.

"I will not sign a document that puts one penny of taxpayer money on the line for one penny of cost overruns," Walsh told reporters at a hastily announced press conference Monday morning.

Reports over the weekend detailed rumors that the USOC wanted Walsh and Gov. Charlie Baker to back the bid more strongly.

The announcement seemed to come in response to those reports, as Walsh said he hadn't talked to the USOC, but cited newspaper stories several times that reporting pressure.

Asked if the bid was over, Walsh replied, "You'll have to ask Boston 2024."

Walsh, an early and ardent backer of the bid, whose operations at times seemed to mesh with those of City Hall, said he refused to mortgage the future of the city away.

"We didn't need the Olympics, we don't need the Olympics to plan the future of Boston," he said.

Still, Walsh said he didn't regret pursuing the Olympics, and dismissed opposition groups as "about 10 people on Twitter."