The war launched by the United States and Israel against Iran spread across the Middle East and beyond on Monday, with Lebanon's Hezbollah entering the fray and a British air base in Cyprus targeted.

Iran’s army said Monday it targeted US Ali Al Salem air base in Kuwait as well as vessels in the Indian ocean after the killing of the Islamic republic’s supreme leader in U.S. and Israeli strikes.

"Missile units of the army’s ground and naval forces operating from various locations targeted the U.S. Ali Al Salem air base in Kuwait as well as enemy vessels in the northern Indian Ocean over the past hours," the army said in a statement.

Israel and Hezbollah traded fire on Monday, while President Donald Trump vowed to avenge the deaths of U.S. service members and said the war with Iran could last for weeks.

The European Union has warned of the cost to the Middle East of a long war, and said it was reinforcing its naval mission in the Red Sea.

The U.S. military on Sunday said three service members have been killed and five seriously wounded in the operation against Iran -- the first casualties of any kind announced on the U.S. side.

The death toll from an Iranian missile attack Sunday in the Israeli city of Beit Shemesh rose to at least nine people, first responders said, in the deadliest strike in the country since the war began.

The Magen David Adom emergency service said: "In the Beit Shemesh area, MDA EMTs and paramedics have pronounced the deaths of nine" people, as well as 28 others injured, with police saying it was a direct hit on a building.

U.S. President Donald Trump on Sunday said he would "be talking" to Iranian leaders but was vague on the timing and noted that much of the country's leadership was dead.

Cheers in Tehran. Retaliation and mourning by Iran. Protests in some parts of the Muslim world, celebrations in others.

Iranian strikes and drone attacks targeted northern Iraq, where U.S. troops are deployed, as furious protests raged in Baghdad on Sunday over the killing of Iran's supreme leader Ayatollah Ali Khamenei.

France can only "be satisfied" with the killing of Iran's supreme leader Ayatollah Ali Khamenei in U.S.-Israeli strikes, said government spokeswoman Maud Bregeon on Sunday.

Israel's military said Sunday that it was "not aware" of any U.S. or Israeli strike on a school in Iran that Iranian authorities say was hit the previous day, killing over 100 people.