Despite the claim by the United Nations' nuclear watchdog that Iran has accelerated its uranium enrichment program, U.S. intelligence agencies continue to believe that there is no hard evidence that Iran has decided to build a nuclear bomb, a U.S. newspaper reported on Saturday.

Recent assessments by U.S. spy agencies are broadly consistent with a 2007 intelligence finding that concluded that Iran had abandoned its nuclear weapons program years earlier, The New York Times reported.

The conclusion was largely reaffirmed in a 2010 National Intelligence Estimate, and remains the consensus view of America's 16 intelligence agencies, the report said.

In a report released on Friday, the International Atomic Energy Agency (IAEA) said Iran has increased its stockpile of uranium enriched beyond the purity level needed for civilian reactors to generate power. It also said it "continues to have serious concerns regarding possible military dimensions to Iran's nuclear program."

Although American, Israeli and European intelligence officials all agree that Iran has been enriching nuclear fuel and developing some necessary infrastructure to become a nuclear power, the Central Intelligence Agency (CIA) and other U.S. intelligence agencies believe that Iran has not decided to resume a parallel program to design a nuclear warhead, which they believed was essentially halted in 2003.

Iran insists that its nuclear program is only for peaceful civilian purposes.

In his testimony to the U.S. Senate on Jan. 31, James Clapper, head of U.S. national intelligence, stated explicitly that American officials believe that Iran is preserving its options for a nuclear weapon, but there was no evidence that it had made a decision to build a weapon. David Petraeus, the CIA director, agreed to this assessment at the same hearing.

Other senior U.S. officials, including Defense Secretary Leon Panetta and Martin Dempsey, chairman of the Joint Chiefs of Staff, have publicly made similar statements recently.

Critics of the U.S. assessment in Israel and European capitals have criticized the CIA for being overly cautious in its assessment of Iran, because the agency is perhaps overcompensating for its faulty intelligence assessment in 2002 about Iraq's alleged programs to develop mass destruction weapons, which turned out to be non-existent, the newspaper report said.

Some U.S. intelligence officials and outside analysts have another explanation for Iran's enrichment activity, saying Tehran could be seeking to enhance its influence in the region by creating "strategic ambiguity" rather than building a bomb now.

Still, U.S. intelligence analysts acknowledged that their assessment was based on limited information, and divining the intentions of closed societies such as Iran is one of the most difficult tasks for them, the report added.