But, speaking to CNN late Friday night, Iranian ambassador Majid Takht Ravanchi said: "In fact was an act of war on the part of the United States and against Iranian people".
The death of General Soleimani, head of Iran's elite Quds force, in the airstrike at Baghdad airport, which also killed nine others, has sparked an escalation in tensions between America and Iran, including the deployment of thousands of USA troops to the region.
The Iranian ambassador to the United Nations described the killing of one of his country's top generals as an act of war, USA media reported late Friday.
Trump defended the action on Friday, noting that Soleimani was plotting "imminent and sinister attacks on American diplomats and military personnel".
The Iranian regime is lobbying the United Nations in an effort to secure global condemnation of the US strike that took out Iranian military commander Qassem Soleimani earlier this week, describing the strike as a "gross violation" of worldwide law and saying it "reserves its inherent right to self-defense".
The US has already started a war against Iran, not just an economic war but something beyond that by assassinating one of our top generals.
He added: "There will be harsh revenge".
Some marchers carried images of Soleimani and Iran's Supreme Leader Ayatollah Ali Khamenei as well as flags of the Popular Mobilization Forces (PMF), a coalition of Iraqi militias that was pivotal in the country's fight against the Islamic State.
"The United States has the best military by far anywhere in the world".
It directly followed the storming of the USA embassy in Iraq in response to airstrikes on pro-Iranian militia groups in the country which killed up to 27 Hezbollah fighters.
The Iranians also called for the U.N. Security Council to condemn the U.S.
Mr Trump has also faced criticism on home turf, with Democratic presidential candidate Joe Biden saying he had: "tossed a stick of dynamite into a tinderbox", which could leave the USA "on the brink of a major conflict across the Middle East". Some accounts say the rocket landed not far from the USA embassy.
An explosion has rocked Baghdad's heavily fortified Green Zone, where the US Embassy is located.
As tensions continued to escalate, the European Union warned against a "generalised flare-up of violence".
Qays al-Khazali, the commander of Asaib Ahl al-Haq, another PMF militia, said "all fighters should be on high alert for upcoming battle and great victory", Al Jazeera reported.