TEHRAN, Sept. 16 (UPI) -- Iran has improved its centrifuges producing enriched uranium, indicating the country overcame some program challenges, an international watchdog agency said.

In a six-page report, the International Atomic Energy Agency charged that Iranian officials still won't reveal information about the country's past research on nuclear weapon design, The New York Times reported Tuesday. IAEA officials said they failed "to make any substantial progress" in their investigation.

"We seem to be at a dead end," a senior official told the Times. "We would describe it as a gridlock."

The agency report released Monday also said "foreign expertise" may have aided Iran with experiments on a detonator that could be used on a nuclear weapon. Iran, which has denied such activities, has been asked for an explanation.

The report said Iran now runs about 3,800 centrifuges, an increase of several hundred during the past several months. The document indicated Iran upped the efficiency of its centrifuges from about 50 percent to about 80 percent. The agency also criticized Iran for continuing to expand its uranium enrichment program in defiance of U.N. Security Council resolutions.

Iranian officials dismissed the report, saying they expected an escalation of international demands in advance of a possible deal, the Los Angeles Times reported.

"We know that the pressures increase when the issues are going to be resolved," Hassan Qashqavi, spokesman for Iran's Foreign Ministry, said Monday in Tehran.

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