What to know:

• Iran vows revenge for Khamenei killing: “You have crossed our red line and must pay the price,” Iran’s parliamentary speaker, Mohammad Bagher Qalibaf, said in a televised address Sunday. “We will deliver such devastating blows that you yourselves will be driven to beg.” Trump warned that any retaliation would only lead to further escalation.
• Reported deaths: Iranian authorities say hundreds have been killed since the start of the U.S. and Israeli strikes. Eleven people have been killed in Israel overall, and dozens were wounded in a strike that hit a synagogue. The U.S. military says three service members have been killed and five seriously wounded in the Iran operation.
• Strikes were planned for months and feared for weeks: Tensions have soared in recent weeks as the Trump administration built up the largest force of American warships and aircraft in the Middle East in decades.