The United States on Friday reiterated its call for Iran to give a formal response to a UN-backed draft deal over its nuclear program.

"Iran has not responded positively to the IAEA proposed agreement for the provision of nuclear fuel for its Tehran research reactor," State Department deputy spokesman Robert Wood told a news briefing.

"We urge Iran to reconsider the opportunity offered by this agreement to meet the humanitarian needs of its people and to engage seriously with us in a dialogue and negotiations. This remains our consistent objective."

The United States will "take a closer look at what measures we may need to take with regard to Iran," Wood said. But declined to talk about new sanctions against Iran.

"The issue of sanctions has been discussed before. ... There's a window of opportunity for Iran. That window is not going to be open forever."

Senior officials of the U.S., Britain, France, Germany, Russia, China, the so-called P-5-plus-1, and EU high representative will have further meetings in coming weeks to discuss Iran's nuclear issues, according to the spokesman.

On Oct. 1, senior officials from the United States, Britain, Russia, France, Germany and China had talks with their Iranian counterparts in Geneva, during which the Iranian side agreed in principle to ship most of its existing low-grade enriched uranium to Russia and France, where it would be processed into fuel rods with a purity of 20 percent.

The enriched uranium would be transported back to Iran to be used in a research reactor for the manufacture of medical radioisotopes.

The United States, Russia and France have approved a draft agreement presented earlier by IAEA chief Mohamed ElBaradei, but Iran wants amendments and more talks over the issue.

However, Iran's Foreign Minister Manouchehr Mottaki said on Wednesday that Iran will not send out its enriched uranium but considers simultaneous fuel swap on its soil.