WASHINGTON - Iran told the United Nations Security Council and Secretary-General Antonio Guterres on Friday that it reserves its right to self-defense under international law after the United States killed Qassem Soleimani, the top commander of the elite Quds Force of Iran's Revolutionary Guards.

Iranian Ambassador to the UN Majid Takht Ravanchi wrote in a letter that the killing of Soleimani "by any measure, is an obvious example of State terrorism and, as a criminal act, constitutes a gross violation of the fundamental principles of international law, including, in particular, those stipulated in the Charter of the United Nations."

Iran earlier vowed revenge for Soleimani's killing, which American forces carried out on orders of US President Donald Trump.

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The Pentagon said the general had been "actively developing plans to attack American diplomats and service members in Iraq and throughout the region."

On Friday, Secretary of State Mike Pompeo said Soleimani was planning a "big action" that would have "put dozens if not hundreds of American lives at risk."