Iran fired on Israel following Israeli strikes in the Lebanese capital Beirut.
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."
All flights in Iran have been canceled until further notice in the wake of the closure of western Iranian airspace, the nation's Airports and Air Navigation Company announced Monday, according to Iranian state TV.
The only open airport is Mashhad International Airport, which the AANC said will remain open to facilitate people returning from the Hajj pilgrimage.
-ABC News' Somayeh Malekian
Fifteen Iranians were injured in recent Israeli attacks on the country, the head of Iran's emergency medical services said on Monday, according to the semi-official Tasnim News Agency.
Fourteen of the injuries were reported in Mahshahr and one was in Tehran, he said, adding that no fatalities have been reported so far.
-ABC News' Somayeh Malekian
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
President Donald Trump said in a post to social media on Monday that Israel and Iran "are looking to do an immediate CEASEFIRE!"
"Final negotiations on 'Peace' are proceeding, subject to ignorance or stupidity getting in its way," Trump wrote, adding that the U.S. blockade of Iranian ports will remain until a deal is reached.
-ABC News' Fritz Farrow
