An inquiry by the U.N. nuclear watchdog into alleged atom bomb research by Iran has degenerated into a silent standoff a few months after Tehran asserted "the matter is over," U.N. officials said on Wednesday.

"We had gridlock before but until September at least we were talking to each other. Now it''s worse. There is no communication whatsoever, no progress regarding possible military dimensions in their program," a senior United Nations official said.

The nuclear watchdog, the International Atomic Energy Agency (IAEA), meanwhile presented its latest report on Iran, saying it planned to start installing another 3,000 centrifuges early next year, adding to 3,800 already enriching uranium and another 2,200 being gradually introduced.

But its figures showed Iran had not boosted the number of centrifuges regularly refining uranium since reaching the 3,800 level in September. The reason for Iran''s relatively slow progress was unclear, U.N. officials said.

Iran, the world''s No. 4 oil exporter, says its program is for generating more electricity. The West suspects a covert effort to develop the capacity to fuel nuclear weapons.