After Iran conducted an unprecedented missile and drone attack against Israel in response to a deadly strike against its embassy complex in Syria, the Islamic Republic’s top diplomat in the United States issued a strongly worded letter outlining the legal basis behind the operation and a warning against further escalation.

The letter, obtained by Newsweek, was written by Iranian Ambassador to the United Nations Amir Saied Iravani and addressed to U.N. Secretary-General António Guterres and U.N. Security Council President Vanessa Frazier. It officially informed U.N. leadership that, “in the late hours of 13 April 2024, the Islamic Republic of Iran carried out a series of military strikes on Israeli military objectives.”

The document referenced earlier warnings of a “decisive response” to Israel’s killing of seven Iranian military personnel. including two senior Islamic Revolutionary Guard Corps (IRGC) commanders, at an Iranian consular building in Damascus 10 days ago, an act that Iravani argued constituted a violation of the U.N. Charter.

“This action was in the exercise of Iran’s inherent right to self-defense as outlined in Article 51 of the Charter of the United Nations,” the letter said, “and in response to the Israeli recurring military aggressions, particularly its armed attack on 1st April 2024 against Iranian diplomatic premises, in the defiance of Article 2 (4) of the Charter of the United Nations.”