He said the country has never won a battle.
Trump also appeared to extend negotiation offer amid tensions in the Middle East.
In his first reaction after a US airstrike, Trump tweeted: “Iran never won a war, but never lost a negotiation!”.
The strike killed Revolutionary Guard General Qassem Soleimani, head of the elite Quds Force, at Baghdad International Airport.
The strike also killed Abu Mahdi al-Muhandis, the deputy commander of the Iran-backed militias in Iraq, the Popular Mobilization Forces, which recently stormed the US embassy in Baghdad.
Iran Supreme Leader, Ayatollah Ali Khamenei has threatened retaliation.
Iraqi prime minister, Adil Abdul-Mahdi, in his reaction, said the rocket strike would “spark a devastating war in Iraq”.
He declared that the assault by the US was “a brazen violation of Iraq’s sovereignty and blatant attack on the nation’s dignity”.