Iranian Parliament Speaker Ali Larijani said Sunday the killing of senior military commander Qasem Soleimani in a US airstrike was an "outright violation" of the United Nations Charter.
"US President [Donald Trump]'s brutal act is a war crime," he said in an address to parliament cited by the official IRNA news agency.
Larijani said Soleimani's killing has changed the political balance of both the region and the international community.
His death marked a dramatic escalation in tensions between the US and Iran, which have often been at a fever pitch since Trump chose in 2018 to unilaterally withdraw Washington from a 2015 nuclear pact world powers struck with Tehran.
Under the 2015 Vienna agreement, most international sanctions against Tehran were lifted in 2016, in exchange for limitations on Iran's nuclear work. US President Donald Trump's administration however pulled out of the deal.
Iranian Supreme Leader Ali Khamenei, who gave Soleimani the country's highest honor last year, vowed "severe retaliation" in response to his killing. Thousands mourned his death in Iraq, Iran and Gaza.
The Pentagon accused Soleimani of plotting the embassy attack and planning to carry out additional attacks on US diplomats and service members in Iraq and the region.
Qassem Soleimani was the head of Iran's elite Quds Force and the mastermind of its regional security strategy. He was killed early Friday near the Baghdad international airport along with senior Iraqi militants in an airstrike ordered by President Donald Trump. The attack has caused regional tensions to soar and tested the US alliance with Iraq. Fearing escalation, NATO has suspended it's training activities in Iraq, while the British Navy has committed to escort every UK-flagged ship across the Straits of Hormuz.
Showing no signs of seeking to reduce tensions, the US president has since issued a stern threat to Iran on Twitter, saying that the US has targeted 52 Iranian sites that it would strike if Iran attacks Americans or US assets in response to the US drone strike that killed Soleimani. He later added that the US will use 'new' equipment to strike Iran.
The US strike on Soleimani's convoy at Baghdad airport also killed Iranian-backed Iraqi militia leader Abu Mahdi al-Muhandis, and it raised the specter of wider conflict in the Middle East.