Iran and the United States concluded a fifth round of high-stakes nuclear talks in Rome on Friday amid growing skepticism in Tehran about the chances of a deal as Washington hardens its position.

The United States would bear legal responsibility in the event of an Israeli attack on Iranian nuclear facilities, Foreign Minister Abbas Araqchi said on Thursday, following a CNN report that Israel might be preparing strikes on Iran.

Iran’s nuclear facilities are deep underground and heavily fortified. An effective attack by Israel would require U.S. assistance for both mid-air refueling and munitions, according to the February intelligence report.