The head of the U.N. atomic energy agency is urging Iran to keep its commitments under a nuclear deal meant to slow its ability to make nuclear arms, after it recently breached one its obligations.

Yukiya Amano of the International Atomic Energy Agency referred to last week’s IAEA finding that Iran overstepped limits on the amount of heavy water it is allowed to possess for the second time since the agreement’s implementation in January.

Heavy water is a concern because it is used to cool reactors that can produce substantial amounts of plutonium. That, in turn, can be applied to making the fissile core of nuclear warheads.

Amano told an IAEA board meeting Thursday that “such situations should be avoided … to maintain international confidence” in the deal.

(AP)