Boston's bid to host the 2024 Olympics has suffered a blow after city mayor Marty Walsh refused to sign a key bill without more assurances for taxpayers.

Walsh revealed his stance on the matter during a news conference coinciding with a meeting between Massachusetts governor Charlie Baker and the United States Olympic Committee (USOC) on Monday. The USOC require the go-ahead from all city and state leaders before it confirms a bid.

"This is a commitment I cannot make without assurances that Boston and its residents will be protected," Walsh said. "I refuse to mortgage the future of the city away. I refuse to put Boston on the hook for overruns. And I refuse to commit to signing a guarantee that uses taxpayer dollars to pay for the Olympics."

Rome, Hamburg, Paris and Budapest have all outlined plans to apply to become the 2024 Olympic host, with eight other cities currently considering bids.