TEL AVIV, Israel — President Donald Trump said the U.S. military struck three sites in Iran, directly joining Israel’s effort to decapitate the country’s nuclear program in a risky gambit to weaken a longtime foe. The strikes happened Saturday amid Tehran’s threat of reprisals that could spark a wider regional conflict. There was no immediate acknowledgment from the Iranian government of any strikes being carried out. Iran’s state-run IRNA news agency reported early Sunday that attacks targeted the country’s Fordo, Isfahan and Natanz nuclear sites. The agency did not elaborate. The decision to directly involve the U.S. in the war comes after more than a week of strikes by Israel on Iran.