Russia raised eyebrows in February when it announced its intention to sell deadly Sukhoi Su-30 fighters and T-90 tanks to Iran. This did not sit well with the United States, which has gone from saying it's simply forbidden by United Nations Security Council Resolution 2231 – the controversial Iran nuclear deal – to saying it'd block the deal outright, using its veto power as a member of the UN Security Council.
"The sale of Su-30 fighter aircraft is prohibited under UNSCR 2231 without the approval of the UN Security Council and we would block the approval of any sale of fighter aircraft under the restrictions," said US Under Secretary of State for Political Affairs Thomas Shannon during a hearing of the Senate Foreign Relations Committee, The Washington Post reports.
And based on a cursory reading of the bill, it appears Under Secretary of Shannon is correct. According to the UN Security Council's website, paragraph five of annex B says "all States may participate in and permit, provided that the Security Council decides in advance on a case-by-case basis to approve...the supply, sale or transfer" of "battle tanks, armored combat vehicles, large caliber artillery systems, combat aircraft, attack helicopters, warships, missiles or missile systems."
Emphasis ours. Russia, for its part, doesn't appear to be reading the same agreement.
"'The UN Security Council's Resolution 2231 has not banned sale of these military equipment to Iran," the chief of the Russian Foreign Ministry's Administration for Security and Disarmament Mikhail Oliyanov told Iran's state-run Islamic Republic News Agency. "We are of the opinion that the possible sale of Sukhoi-30 fighter jets and T-90 tanks of Russia to Iran have not been prohibited in Resolution 2231 and this resolution has permitted Iran to purchase such military hardware."
For those that need a refresher, the Su-30 is an upgraded version of Russia's old-but-still-deadly Su-27 Flanker. It's an all-weather, multi-role, fourth-generation fighter and would be among the most advanced aircraft in the Islamic Republic Iran Air Force, alongside the MiG-29. Aside from the MiG, most of Iran's fighter complement are American-made aircraft, delivered while the Shah still reigned.
With two radically different interpretations of a UN Security Council resolution, it's almost certain that there will be a rather serious showdown at UN headquarters in the very near future.