Iranian missiles struck Israel this evening, causing damage to at least seven sites around Tel Aviv, officials said. Some of the missiles were intercepted by Israel’s Iron Dome system, but video showed at least one large explosion in Tel Aviv and at least 40 people were injured, some critically, according to a tally from three hospitals.

Israel’s defense minister said Iran had “crossed a red line” by firing on civilian areas.

The attacks were the beginning of Iran’s retaliatory campaign after Israeli strikes last night devastated Tehran’s military chain of command and hit critical nuclear facilities. Years of intelligence collection, infiltration of Iran with commandos and weapons, and tracking of targeted commanders and scientists made Israel’s attacks possible.

The U.S. military said it was helping Israel to intercept some of the ballistic missiles. American officials have said the U.S. had not taken part in Israel’s attacks on Iranian targets, but the Pentagon had already begun moving more assets to the region to help defend American troops.

Israel’s leader, Benjamin Netanyahu, has long cast Iran’s Shiite Islamist regime as an existential threat to Israel. He described last night’s attack as necessary to prevent Tehran from getting a nuclear weapon. It may take days or weeks to determine how successful they were, but Netanyahu vowed that the fighting would last “as many days as it takes.”

For more: Here are maps and photos of Israel’s attacks, and a look at the generals and scientists who were killed in the strikes.

Analysis: President Trump’s diplomacy goals are in tatters, and Iran is in its worst position in decades.