After months of intense discussions, negotiations between a New York antiquities collector and the Italian government have bogged down over a demand that she never be pursued by Italy again, several people close to the talks say.

Italy is seeking the return of nine artifacts from the collector, Shelby White, contending that they were looted from its soil.

Lawyers for both sides had been optimistic earlier this year that a deal could be struck. But an impasse developed over Ms. White’s insistence that in exchange for the objects, the Italian Culture Ministry grant her immunity from legal action of any kind and promise not to go after anything else she owns or acquires in the future, people familiar with the talks said.