The Israeli Air Force conducted strikes on military targets in central and Western Iran on Monday morning local time, Israel Defense Forces said in a statement.Why it matters: The strikes, in retaliation for an Iranian missile attack against Israel, mark a new phase in a growing escalation that started on Sunday morning. This is the first time Israel has struck Iran since the April 8 ceasefire. Iran had threatened to expand its attacks and target U.S. bases in the region if Israel retaliated. Further exchanges of fire could unravel the negotiations between the U.S. and Iran and lead to the resumption of the war.President Trump told Israeli Prime Minister Benjamin Netanyahu several hours before the strikes to stand down and refrain from retaliating. Between the lines: A U.S. official said the Israel strikes were "relatively limited" in their scope.State of play: Explosions were heard in the Iranian cities of Tehran, Karaj, Isfahan, Tabriz and Kermanshah, according to Iranian state media. Iran closed its airspace around Tehran's Imam Khomeini International Airport following the strikes.Go deeper: Israel strikes Beirut after Hezbollah attack, risking Iran responseEditor's note: This article has been updated with comment from a U.S. official and details of Iran closing airspace.