Her decision was a blow for the city`s Olympic committee which had hoped to change her mind. But officials said she had failed to turn up to a meeting.
Rome last hosted the Games in 1960 and also pulled out of the bidding for the 2020 Olympics for financial reasons.
Boston and Hamburg have already dropped out of the running for the 2024 Games. Germany has not hosted a games since 1972, and Hamburg`s decision to pull out was made in a referendum.
Paris, Los Angeles and Budapest are still vying to host the Games. The remaining candidates must confirm their application and the endorsement of local public leaders by 7 October.
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