The Pentagon will deploy a few thousand additional U.S. troops and more fighter jets to the Middle East, defense officials said Monday, as part of the Biden administration’s scramble to prevent the conflict between Israel and Iran’s proxies from exploding into a regionwide war.

The infusion of forces, which also include air-defense units, will add to the tens of thousands of American personnel already on high alert there, said Sabrina Singh, a Pentagon spokeswoman. The moves were ordered by Defense Secretary Lloyd Austin after Israel last week used a series of airstrikes around Beirut to kill Hezbollah leader Hasan Nasrallah, and as U.S. officials anticipated that Israel could soon launch a limited ground incursion into Lebanon.

Singh told reporters that to further boost the number of personnel in the Middle East the Pentagon will extend some deployed units that were scheduled to rotate home and send additional forces to augment them, including squadrons that fly F-16, F-15E and F-22 fighters and A-10 attack jets. Austin also issued prepare-to-deploy orders for an unspecified number of other units that are in the United States, she said.

Singh linked the additional deployments directly to rhetoric from senior Iranian officials, including Ayatollah Ali Khamenei, who has called for all Muslims to stand with Hezbollah as it confronts Israel. Writing on social media over the weekend, he declared that “the blows struck by the Resistance Front on the worn-out, deteriorating body of the Zionist regime will become even more crushing.” The resistant front is a reference to the network of militant proxy forces that Iran backs across the region, including Hezbollah in Lebanon, Hamas in Gaza, the Houthis in Yemen, and several militia forces in Iraq and Syria.

Next week, Israel will mark the first anniversary of the attack by Hamas that spawned the ongoing war in Gaza. Hezbollah, acting in solidarity with Hamas, has routinely traded fire with Israel in the months since, forcing large-scale evacuations on both sides of their shared border. But over the past two weeks, the conflict has escalated drastically as Israel has undertaken an aggressive operation to decapitate and degrade its adversary in Lebanon.

The speed and scope of Israel’s campaign against Hezbollah, a longtime U.S.-designated terrorist organization, has taken Biden administration officials by surprise. Austin, Singh said, learned of the operation to kill Nasrallah as it was underway and was “caught off-guard” by it. She added that the defense secretary had a “firm” conversation with his Israeli counterpart, Defense Minister Yoav Gallant, afterward.

While Iranian-backed forces have launched more than 170 attacks against U.S. forces stationed in Iraq, Syria and Jordan over the last year, as of Monday morning none had been reported since Nasrallah’s killing, defense officials said.

The Pentagon has maintained a significant amount of firepower at sea throughout the Middle East crisis, and Austin on Sunday extended the deployments of several warships, including those assigned to the Abraham Lincoln Carrier Strike Group and the Wasp Amphibious Ready Group.

The strike group, led by the aircraft carrier USS Abraham Lincoln, is in the Arabian Sea and accompanied by a few Navy destroyers. The amphibious group comprises a three-ship flotilla of sailors and Marines and has been deployed in the eastern Mediterranean Sea since the summer. The 24th Marine Expeditionary Unit aboard those vessels is trained in evacuation operations and seemingly poised to respond if U.S. officials order an evacuation for Americans in Lebanon.