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

The autonomous surface sea drone used to rescue the two Apache crewmembers picked them up and transported them to another location on the water where they were then hoisted up to a helicopter for further transport, according to a U.S. official.

The Iranian military's Khatam Al-Anbiya Central Headquarters said in a statement on Monday that Iran's retaliation against Israel for attacks on Lebanon has concluded, but warned that if hostilities continue, Iran's response will be more severe.

"A painful response was delivered to the Israeli regime, and the suspension of armed forces operations is announced," the statement said, according to Iranian state media.

"If the aggressions and provocations continue, including in southern Lebanon, much more severe and decisive actions than before will follow," the statement added.

-ABC News' Somayeh Malekian