WASHINGTON (NEXSTAR) – Fears of a regional war are growing as tensions between Israel and Lebanon ratchet up and the U.S. prepares for an expanded conflict.

The U.S. is urging its citizens to get out of Lebanon.

Iran has vowed to strike back after Israeli operations killed top Hamas commanders in Lebanon and Tehran.

“When the Supreme Leader says he’s going to avenge we have to take that seriously,” National Security Council Spokesperson John Kirby.

 U.S. officials say they are expecting some kind of military reprisal to happen.

 “We got to make darn sure that we’re ready and we have the capabilities in the region to be able to help Israel defend itself,” said Kirby.

For months, there’s been fighting between Israel and Lebanon along their shared border but with recent escalation, officials fear that could become a major new front in Israel’s war against Hamas and potentially Hezbollah.

“We’ve been very, very consistent about not wanting to see this war escalate and get broader. We’ve also been very, very consistent about proving not just with words, but with action, that we’re going to stand up and defend Israel,” said Kirby.

The White House and lawmakers say the U.S. military is ready to respond to Iran or any other threat.

“They need to know that we’re willing to use it and we will immediately if they go after Israel for taking out the Hamas leader,” said Sen. Markwayne Mullin (R-Okla.)

President Joe Biden will meet with his national security team to discuss the situation Monday afternoon.