NATO Secretary General Jens Stoltenberg on Tuesday welcomed the comprehensive landmark agreement reached between Iran and the international community.

Commending all parties for their perseverance in a statement, he said, "This agreement represents a historic breakthrough which, once fully implemented, will strengthen international security."

Stoltenberg added it was critical for Iran to implement the provisions of the agreement and to fulfill all its international obligations and advance security in the region and beyond.

The agreement was clinched between Iran and the P5-plus one group, namely Britain, China, France, Russia and the United States plus Germany, after more than two weeks of tough bargaining in the Austria capital city of Vienna.

NATO allies had cooperated with Russia in efforts to try to reach a deal with Iran on nuclear weapons, though it has suspended all practical cooperation with Russia in the wake of the Ukraine crisis.

In a speech at the start of the meetings of NATO defense ministers in June, Stoltenberg said: "Russia being member of the Security Council in the UN is a global actor where several NATO allies in different capacities and different frameworks are working with Russia."