[en] On 29 December 1972 the Agency and the Governments of the United States of America and Yugoslavia amended by letter of agreement Sections l(i), 4 and 5 of the Third Supply Agreement, concluded in connection with the Agency's assistance to Yugoslavia for the continuation of a research reactor project and reproduced in document INFCIRC/32/Add. 3, to provide for the transfer to Yugoslavia of up to a total net amount of 4800 grams of uranium-23 5 contained in uranium enriched up to approximately 70 per cent in the isotope uranium-235, and for payment by Yugoslavia within 20 days from the date of the invoice received from the Agency and by the Agency within 30 days from the date of the invoice received from the United States Atomic Energy Commission