The U.S. military said on Sunday it was increasing its air support capabilities in the Middle East and putting troops on a heightened readiness to deploy to the region as it warned Iran against expanding the ongoing conflict.

The announcement came two days after President Joe Biden directed the Pentagon to adjust U.S. force posture in the Middle East amid intensifying concern that Israel's killing of the leader of Iran-backed Hezbollah could prompt Tehran to retaliate.

"The United States is determined to prevent Iran and Iranian-backed partners and proxies from exploiting the situation or expanding the conflict," Pentagon spokesperson Major General Patrick Ryder said in a statement.

He also cautioned that if Iran or groups Tehran backs "use this moment to target American personnel or interests in the region, the United States will take every necessary measure to defend our people."

The Pentagon statement offered few clues as to the size or scope of the new air deployment, saying only that "we will further reinforce our defensive air-support capabilities in the coming days."

Israel struck more targets in Lebanon on Sunday, pressing Hezbollah with new attacks after killing the group's leader, Sayyed Hassan Nasrallah, and a string of its other top commanders in an escalating military campaign.

The strikes have dealt a stunning succession of blows to Hezbollah after almost a year of cross-border fire, killing much of its leadership and revealing gaping security holes. But it has also raised questions about Washington's publicly declared goals of containing the conflict and safeguarding U.S. personnel throughout the Middle East.

White House national security spokesperson John Kirby said on Sunday that the United States is watching to see what Hezbollah does to try to fill its leadership vacuum, "and is continuing to talk to the Israelis about what the right next steps are."

The U.S. State Department has yet to order an evacuation from Lebanon. But last week, U.S. officials told Reuters the Pentagon was sending a few dozen additional troops to Cyprus to help the military prepare for scenarios including an evacuation of Americans from Lebanon.

The Pentagon said U.S. forces were being made ready to deploy, if needed.

"[Austin] increased the readiness of additional U.S. forces to deploy, elevating our preparedness to respond to various contingencies," Ryder said in a statement.