The European Union formally imposed new sanctions against Iran on Monday, setting an embargo on imported Iranian oil to all European countries.
Leaders are also freezing the assets of the Iranian Central Bank.
The sanctions are meant to force the Islamic Republic to resume talks on its nuclear program. At the very least, it shows Europe is unified, with 27 ambassadors working together to reach the agreement.
British Foreign Secretary William Hague called the embargo part of an "unprecedented set of sanctions."
"I think this shows the resolve of the European Union on this issue," Hague said.
German Foreign Minister Guido Westerwelle said it was critical that action be taken.
"This is not a question of security in the region," he said. "It is a question of security in the world."
Iran still shows no signs of backing down. The Iranian regime previously threatened to close the strategic Strait of Hormuz in the Persian Gulf if the U.S. and the E.U. implemented severe sanctions against its oil exports.
Iran's navy recently carried out military exercises in the strait.