U.S. President Barack Obama said on Tuesday that the United States and the international community await "a formal and authoritative message" from Iran to the International Atomic Energy Agency (IAEA).

Obama made the remarks in a phone call with Turkish Prime Minister Rejep Tayip Erdogan.

Obama acknowledged the efforts of Turkey and Brazil, but stressed the international community's continuing and fundamental concerns about Iran's overall nuclear program.

He indicated that negotiations on a new UN Security Council resolution will continue, noting that Iran's persistent refusal to meet with the P5+1 on its nuclear program does not build confidence.

The P5+1 refers to the five permanent members of the UN Security Council -- Britain, China, France, Russia and the United States -- plus Germany.

Iran signed an agreement with Turkey and Brazil in Tehran on Monday, by which it will ship most of its low enriched uranium to Turkey in exchange for the 20-percent uranium fuel needed for its Tehran reactor.

Iran's move came one day before the five permanent members of the UN Security Council and Germany announced their agreement on a draft resolution proposing new sanctions against Tehran.