Iran's president Masoud Pezeshkian said in a post on X following Trump's briefing that Iran "will stand firm against any pressure or threat". BBC reported.
US Central Command (Centcom) said on Wednesday night that forces had begun launching strikes at 17:15 Eastern Time (22:15 BST) against "multiple targets" in Iran.
It added in a post on X that the strikes were "in response to Iran's unwarranted and continued aggression".
The US also launched strikes on Iran on Tuesday after Trump said Iran had downed a US Army helicopter.
Iran's Islamic Revolutionary Guard Corps (IRGC) said it responded with strikes on US bases in the region.
Trump reiterated a call for Iran to "sign a deal" during his briefing on Wednesday, while US Defence Secretary Pete Hegseth told reporters later that day that bombs would be "dropping on key facilities in Iran".
He added: "President Trump said we will be hitting Iran hard and we will be".
Earlier on Wednesday Trump wrote on his social media account: "They've taken too long to negotiate a deal that would have been great for them, now they will have to pay the price!!!"
He said Iran had been "completely defeated" militarily.
Iran's foreign ministry spokesman Esmaeil Baqai meanwhile accused the US of "damaging this diplomatic process through the contradictory messages it sends, its repeated shifts in positions and demands, and, worst of all, through repeated violations of the ceasefire".
