Officials from six world powers have expressed disappointment at Iran's refusal to accept a proposal to send its uranium abroad for further enrichment.
European Union official Robert Cooper says Iran has not responded "positively" to the U.N.-brokered enrichment plan.
Cooper spoke after representatives from Germany and the five permanent members of the U.N. Security Council (the United States, Britain, France, China and Russia) held talks Friday in Brussels about Iran's nuclear program.
Iran's Foreign Minister Manouchehr Mottaki has said his country will not process its enriched uranium abroad and will consider only a uranium-for-fuel swap inside Iran.
On Friday, the head of the U.N. nuclear agency, Mohamed ElBaradei, urged Iran to accept the offer. He said he hopes Iran will not miss what he called a "unique but fleeting opportunity."
He also said it is Iran's turn to decide how it wants to proceed on the issue.
U.S. President Barack Obama says his administration has begun talks with its allies on the consequences of Iran's failure to respond to the proposed deal.
Iran has not suspended its uranium enrichment activities, despite three rounds of U.N. Security Council sanctions. Officials at the Brussels meeting say there was no talk of imposing additional sanctions on Iran.
Enriched uranium produces fuel that can be used for civilian purposes or, in highly enriched form, for nuclear weapons.
Iran says its nuclear program is for peaceful purposes.
Some information for this report was provided by AFP, AP and Reuters.