The head of Iran's Atomic Energy Organization says the country has transferred 11 tons of heavy water to Oman.
"Eleven tons of heavy water has been sent to Oman and the other party has announced its readiness for the purchase," Ali Akbar Salehi said on November 22, according to the IRIB news agency.
Heavy water is used in certain types of reactor which can produce plutonium that is used in a nuclear bomb.
Earlier this month, the International Atomic Energy Agency said Iran's stocks of heavy water had reached above the 130-ton level set out in the nuclear deal signed by Tehran and world powers last year.
Atomic Energy Organisation spokesman Behrouz Kamalvandi insisted last week that Tehran had not breached the agreement.
"We were required to put on the international market any excess over 130 tons, and so far we have sold 70 tonnes," Kamalvandisaid.