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Sirens sound across Israel Sunday morning, signaling millions to head into bomb shelters hours after a United States military strike on three nuclear enrichment facilities in Iran.

Israel Defense Forces announced Iran had launched about 30 missiles at Israel.

At least 21 people were wounded as Iranian missiles made impacts in four sites across Israel: in Haifa, Tel Aviv, Be’er Yaakov and Nes Ziona, according emergency response.

Searches were underway for people believed to be trapped under the rubble of a collapsed building in Tel Aviv, local media reported.

From the White House at 10 p.m. EST on Saturday, President Donald Trump said that U.S. warplanes had carried out a “very successful attack” on three key nuclear sites in the Iranian regime, including Fordow, Natanz, and Isfahan.

While now directly involving the United States in  war between Iran and Israel that has been going on more than a week, Trump said the objective was to destroy Iran’s nuclear enrichment capabilities and stop the nuclear threat posed by Iran.

“Tonight I can report to the world that the strikes were a spectacular military success,” Trump said, adding that the nuclear enrichment facilities were “completely and totally obliterated” in air strikes that did not put any US military in harm’s way.

While his words had signaled the hope that the conflict could be over, Trump threatened more attacks on Iran if it decides to retaliate.

“This cannot continue,” Trump said. “There will be either peace, or there will be tragedy for Iran far greater than we have witnessed over the last days,” he added, referring in part to attacks that Israel has carried out on Iran.

While the U.S. and Iran have fought deadly proxy battles for nearly a half-century in Lebanon, Yemen, the Strait of Hormuz and elsewhere, Trump’s action was the first significant U.S. military strike on Iranian soil since the 1979 overthrow of the U.S.-backed shah of Iran, Mohammad Reza Pahlavi.

Trump’s decision to enter the conflict raises immediate questions about how Iran or its proxies may react, even as scores of Israeli strikes have left Iranian military capabilities diminished. Iran has threatened to retaliate against U.S. troops, tens of thousands of whom are deployed throughout the Middle East in countries such as Bahrain, Iraq, Kuwait, Saudi Arabia and the United Arab Emirates.

While most congressional Republicans and some pro-Israel Democrats are praising President Trump’s strikes on Iranian nuclear facilities, some members of Congress called it “unconstitutional,” saying that the President needed Congressional approval for such a provocative use of military force.