Israel is preparing for a direct attack from Iran on southern or northern Israel as soon as the next 24 to 48 hours, a person familiar with the matter told The Wall Street Journal on Thursday night.
A person briefed by the Iranian leadership, however, said that while plans to attack are being discussed, no final decision has been made.
Iran has publicly threatened to retaliate for an attack last week in Damascus, Syria, that Tehran said was an Israeli air strike on a diplomatic building and in which top Iranian military officials, including a senior member of the Islamic Revolutionary Guard Corps, were eliminated.
Earlier on Thursday, Iranian sources told Reuters that Iran has signalled to Washington that it will respond to the attack attributed to Israel on its Syrian embassy in a way that aims to avoid major escalation and it will not act hastily.
Iran's message to Washington was conveyed by Iranian Foreign Minister Hossein Amir-Abdollahian during a visit on Sunday to the Gulf Arab state of Oman, which has often acted as an intermediary between Tehran and Washington, the sources said.
Later, a US official told Reuters that the United States expects an attack by Iran against Israel but one that would not be big enough to draw Washington into war.
CBS News reported last week that the US has picked up intelligence on what an Iranian retaliatory strike might look like.
According to the report, the American intelligence indicates that Iran is planning a retaliatory attack that would include a swarm of Shaheed loitering drones and cruise missiles.
Another report in The New York Times cited two Iranian officials who said that Iran had placed all its armed forces on full high alert and a decision had been made that Iran must respond directly to the strike attributed to Israel in Damascus, in order to create deterrence.