US fears Iranian retaliation: "Working with Israel on defense"

After the assassination of Hezbollah Secretary-General Hassan Nasrallah, the Biden administration expressed concern on Monday morning about Iranian retaliation. A senior U.S. official told CNN that a defense plan is being formulated for a possible attack.

Last night, Biden said that "an all-out war must be avoided." Against this backdrop, Iran sent a threat: "Israel's crimes will not go unanswered."

Hezbollah Deputy Secretary-General Naim Qassem said in his first speech since the assassination: "We have lost a leader and a brother. The fighting will be long, but we are prepared for a ground incursion by Israel."

The U.S. official quoted declined to say what kind of attack would come from Iran, or to specify the U.S. military's moves. The Biden administration headed Israel's multinational defense in April, when Iran launched more than 300 drones and missiles at Israel in response to an attack on senior IRGC officials at the Iranian embassy in Syria.

Meanwhile, Russia today condemned Nasrallah's assassination: Kremlin spokesman Dmitry Peskov said the move would "lead to significant instability in the region."

* Channel 13 contributed to this article.