Zarif said U.S. President Donald Trump had displayed a lack of respect for international law by threatening Iran's cultural sites.
"This is state terrorism," Zarif said of the killing of Qassem Soleimani, commander of the Revolutionary Guard's Quds Force, in a U.S. drone attack in Baghdad last week.
"This is an act of aggression against Iran, and it amounts to an armed attack against Iran, and we will respond. But we will respond proportionately - not disproportionately ... We are not lawless like President Trump."
Trump said on Saturday the United States was ready to strike 52 Iranian sites, including some important to Iranian culture, if Iran attacked U.S. assets or Americans.
On Sunday, he said the United States would strike back "perhaps in a disproportionate manner" if Iran attacked any American target.
Zarif said Trump had shown the world he was "prepared to commit war crimes, because attacking cultural sites is a war crime. Disproportionate response is a war crime."
Soleimani was responsible for building up Tehran's network of proxy armies across the Middle East and he was a key figure in orchestrating Iran's long-standing campaign to drive U.S. forces out of its neighbor Iraq.
Zarif said Washington should wake up to the reality that "the United States cannot stay in this region with the people of the region not wanting it any more."Asked if it was worth speaking to Trump, Zarif said: "It doesn't need speaking. He has to realize that he has been fed misinformation. And he needs to wake up, and apologize. He has to apologize, he has to change course."