CENTCOM said Iran struck down an Army Apache helicopter on Monday.
President Donald Trump announced "major combat operations" against Iran on Feb. 28, with massive joint U.S.-Israeli strikes targeting military, government and infrastructure sites.
Following the announcement of a two-week ceasefire, initial U.S.-Iran talks in Pakistan in April failed to reach a peace deal.
Trump later announced the open-ended extension of the ceasefire and the continuation of a U.S. blockade until negotiations are concluded "one way or the other."
In response to the U.S. strikes, Iranian Foreign Minister Abbas Araghchi said that Iran's military "will leave no attack or threat unanswered."
"Leave our region if you want to be safe," he said.
ABC News chief Washington correspondent Jonathan Karl was on the phone with President Donald Trump just as CENTCOM announced the retaliatory attack against Iran.
"I think it's very important to respond. They shot down a helicopter, and we are responding as we speak," Trump said.
"I believe in responding in a strong manner. I always have throughout my life. And we have a deal that was very good, and probably will [still be]," the president continued. "This is a response to what they did they did with our helicopter last night, and I believe the response should be very strong, very powerful, and that's what this one is."
As the call ended, CENTCOM announced the attack.
U.S. forces have begun launching "self-defense" strikes in response to Iran's attack on a U.S. Army Apache helicopter, U.S. Central Command said.
The strikes began at 5 p.m. ET, it said.
The U.S. Apache attack helicopter that crashed near the coast of Oman overnight was brought down by an Iranian drone, two U.S. officials familiar with the Pentagon’s latest assessment tell ABC News.
The investigation has not yet determined whether Iran intended to use the drone to attack the helicopter, they added.
The drone involved in the incident is the same type Iran typically uses to target ships transiting the Strait of Hormuz, one official said.
-ABC News' Shannon K. Kingston and Luis Martinez
