If Israel strikes back, the response speed from Iran "will be less than a few seconds," said Ali Bagheri Kani, the deputy foreign minister of Iran for political affairs.

Maj. Gen. Pat Ryder, the Pentagon press secretary, said Monday that Iran did not give the U.S. an advanced notice of its attack on Israel.

"I think what you're asking was did Iran give us a heads up? No, they did not," Ryder said, without indicating whether the U.S. learned of Iran's plans through allies.

Ryder said U.S. forces in the Middle East intercepted dozens of missiles and unmanned aerial vehicles when Iran and its proxies launched attacks in retaliation for Israel's strike earlier this month on the Iranian Consulate in Damascus, Syria, that killed an Iranian military leader.

Ryder repeated assessments that 99% of incoming Iranian fire was intercepted by Israel and its partners, but he wouldn't confirm reports that half of the launches failed to get off the ground.

Secretary of Defense Lloyd Austin, Ryder said, has spoken with Israeli Defense Minister Yoav Gallant three times since the attack.

"During their most recent call yesterday, the two leaders reviewed the successful combined operation by the United States, Israel and their partners to defend Israel from these unprecedented attacks by Iran and its proxies and emphasize that while the United States does not seek escalation, we will continue to take all necessary action to defend Israel and U.S. personnel," Ryder said.

Asked whether the response to Iran's attack depleted the air defense resources of Israel and its partners, Ryder declined to answer.

"As we demonstrated this weekend, we have the capability and the capacity to defend Israel and to defend our forces in the region," he said.

-ABC News' Chris Boccia and Matt Seyler

As Israel's Chief of the General Staff Herzi Halevi met with troops at the Nevatim Airbase, where Iranian missiles struck over the weekend, he said Israel is weighing possible response actions.

"As we look forward, we weigh our steps, and this launch of so many missiles, cruise missiles, UAVs to the territory of the State of Israel will be met with a response," Halevi said.

-ABC News’ Jordana Miller

As Israel on Monday weighed its response to Iran’s weekend attack, the U.S. is privately telling officials there: If Israel strikes back militarily, it will do so alone.

It's an unusual message for a close ally that's spent decades receiving more U.S. military aid than any other country in the world and whose relationship with America is often described as "ironclad."

But after months of Israel acting on its own in Gaza -- and facing tough criticism from the U.S. and other allies that its military operations have gone too far – the Biden administration made clear the U.S. wouldn't participate in offensive military operations against Iran, fearing a broader war in the Middle East.

"We believe Israel has freedom of action to protect itself and defend itself," a senior administration official told reporters shortly after Iran's attack ended. "That's a long-standing policy, and that remains."

When asked by a reporter if the U.S. would help Israel counter with offensive military operations, the official said no.

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-ABC News’ Anne Flaherty

White House National Security Council spokesman John Kirby told ABC's "Good Morning America" Sunday that any response to Iran's Saturday night attack is up to Israeli forces.

But Kirby stressed that President Joe Biden does not want the situation to escalate or have the U.S. drawn further into any conflict.

When asked by ABC News' Whit Johnson about a response from Israel, Kirby said that it is up to the Israeli government to decide how to respond. He added that "the damage was extremely light," and the defenses in place proved Israel can defend itself.

"I won't speak for the Israelis. It's going to be up to them to decide whether and how they'll respond to this," Kirby said. "They showed last night, an incredible military capability on their own, but certainly in concert with friends."

When pressed about reports that Biden told Israeli Prime Minister Benjamin Netanyahu the U.S. would oppose a counterattack on Iran, Kirby said it was "not an accurate reading" of the president's message. He emphasized that the White House does not "want to see the situation escalate further."

"The president understands the prime minister runs a government for a sovereign state of Israel, and that they'll decide whether and how they're going to respond to what Iran did last night," Kirby said.

Kirby reiterated the White House's message that the president will do "whatever he has to protect our troops and our facilities, our people in the region." He said there is no current threat to U.S. service members and facilities, noting that more U.S. forces moved into the region after Oct. 7 to help defend Israel and shipping channels in the Red Sea.

"We're going to obviously be vigilant to any potential threat to our forces in the region," Kirby said. "But the president has been clear we are not looking for a wider war. We're not looking for a second front or a third front. We're not looking to see escalation and we're certainly not looking for a war with Iran."

Kirby added that good intelligence about the attack helped the U.S. and Israel prepare.

"We've been watching as closely as we could the intelligence picture, we had a pretty good indication of the size and the scale and the scope of what Iran was planning," Kirby said. "That is why, because we had a good sense of what they were going to do and with how much, we were able to really help Israel knock down almost everything that Iran threw at them."