Iran has told the U.N. nuclear agency that it is running a new, previously undeclared, facility to enrich uranium, officials told The Associated Press Friday.

Iran is under three sets of U.N. Security Council sanctions for refusing to freeze enrichment. The officials said that Iran revealed the existence of a second enrichment plant in a letter sent Monday to International Atomic Energy Agency chief Mohamed ElBaradei.

It had previously said it was operating only one plant, which is being monitored by the IAEA.

The Islamic Republic insists that it has the right to the activity to generate fuel for what it says will be a nationwide chain of nuclear reactors.

But because enrichment can make both nuclear fuel and weapons-grade uranium, the international community fears Tehran will use the technology to generate the fissile material used on the tip of nuclear warheads.

The revelation further burdens the chances of progress in scheduled Oct. 1 talks between Iran and six world powers.

At that planned meeting — the first in more than a year — the five permanent U.N. Security Council members and Germany will be pressing Iran to scale back on its enrichment activities. But Tehran has declared that it will not bargain on enrichment.