The United States "would encourage the Iranians -- and I know many are -- not to move down that road because the consequences could be quite cataclysmic, particularly for Iran," a senior US official told reporters on customary condition of anonymity.

President Joe Biden earlier Friday said that a ceasefire in the 10-month Gaza war was closer than ever after two days of talks in Qatar at which US mediators presented a proposal to narrow gaps.

"It was Hamas, a proxy of Iran, that started this war on October 7, and it would be ironic if Iran was do something to derail what we think is the best opportunity at a very comprehensive ceasefire and hostage release deal that we have had in many months," the US official said.

Iran has warned Israel of a response to the July 31 strike in Tehran that killed Hamas political chief Ismail Haniyeh, for which Israel is widely suspected but has not claimed responsibility.

Israeli Foreign Minister Israel Katz said earlier Friday in a joint meeting with his British and French counterparts that he expected support in "attacking significant targets" inside Iran if the Islamic Republic strikes Israel.

Asked about Katz's comments, the US official said only that the United States, with Britain and France, was preparing for "every possible contingency."

"We are going to do everything that is needed to defend Israel against any attacks from Iran," he said.