Nuclear power plant (illustration)
Nuclear power plant (illustration)Thinkstock

A State Department official admitted on Thursday he was unsure of the precise location of tons of low-enriched uranium shipped out of Iran on a Russian vessel as part of the nuclear agreement with the West.

Speaking to the House Foreign Affairs Committee and quoted by AP, Ambassador Stephen Mull, the lead U.S. official overseeing the deal’s implementation, explained that the stockpile is a Russian custody issue.

He said, however, the U.S. is confident the material will be controlled properly.

“We obviously have had many differences for many years with Russia,” Mull said, according to AP. “But one of the features of our relationship is pretty close cooperation and protection of nuclear material.”

In late December, Iran sent a major shipment of low-enriched uranium materials to Russia, described by the United States as 25,000 pounds of "low-enriched uranium materials."

This paved the way for the International Atomic Energy Agency’s (IAEA) subsequent announcement that Iran met its initial obligations under the terms of the nuclear deal, enabling the implementation of the agreement and lifting of the sanctions on Iran.

Following Thursday’s hearing, a senior administration official told AP the Iranian stockpile is in Russia, where it will be stored in a secure location. The official was not authorized to speak publicly and requested anonymity.

But critics of the nuclear deal seized on the shipment’s status as an example of the agreement’s flaws. Rep. Chris Smith (R-NJ), said in a statement that it’s “outrageous and unbelievable” that Russia is being trusted to be the repository for such sensitive material.

Russia is a close ally of Iran, said Smith, who added that he is unaware of a requirement in the nuclear agreement that requires Russia to declare where the material will be stored and how it will be safeguarded.

But Mull stressed that the United States does “not have concerns about Russian custody of this material”. What’s important, he said, is that it not be returned to Iran.

Mull said there are sufficient monitoring systems in place to know if even “one piece of dust of that material goes back.”

The removal of the sanctions on Iran came despite a December 2 report from the IAEA which concluded that Iran made a "coordinated" effort to develop nuclear weapons in the past, although the efforts apparently ended at an early stage.

The UN watchdog had also previously released a report which determined that Iran had violated the terms of its nuclear deal with the West by increasing its stockpile of low-enriched uranium by 460.2 kilograms.