US Secretary of State Antony Blinken told his counterparts from the G7 countries that Iran and Hezbollah could start attacking Israel as early as Monday, US news service Axios reported.
But Blinken, according to Axios, which cited three sources briefed on the call, said it was unclear how Iran and Hezbollah would attack and did not know the exact timing.
There are mounting fears that Israel's war against Palestinian militants in Gaza could escalate into a wider Middle East conflict.
Iran and Hamas have blamed Israel for the killing of Hamas chief Ismail Haniyeh in the Iranian capital, and they, together with Hezbollah, have vowed revenge.
An Israeli strike in Beirut has also killed Fuad Shukr, a senior Hezbollah military commander.
When asked about the Axios report, the State Department referred to a readout of the call, where it said the ministers discussed "the urgent need for de-escalation in the Middle East."
The Pentagon said on Friday it would deploy additional fighter jets and Navy warships to the region.
"The overall goal is to turn the temperature down in the region, deter and defend against those attacks, and avoid regional conflict," Jonathan Finer, the White House's deputy national security adviser, said on CBS' "Face the Nation" program.
The US and Israel are preparing for every possibility, Finer added.
There was a "very close call" of regional conflagration in April, Finer said, when Iran launched an attack on Israeli territory with drones and missiles after what it called an Israeli strike on its consulate in Damascus on April 1 that killed seven officers of the Iranian Revolutionary Guard Corps in the Syrian capital.
