VIENNA — A new U.N. effort to probe suspicions that Iran worked on atomic arms ended on a downbeat note Thursday, with diplomats saying that Tehran refused entry to Iran to a U.S. nuclear expert on the U.N.'s investigating team.

The diplomats also said that the trip this week didn't succeed in advancing a decade of U.N. efforts to investigate suspicions that Tehran worked on such weapons.

Reza Najafi, Iran's envoy to the IAEA, confirmed that an International Atomic Energy Agency staff member was refused a visa. Najafi didn't identify the person, but told Iran's Fars news agency that he had a "particular nationality."

The inquiry is formally separate from U.S.-led talks with Iran focused on long-term caps on Tehran's atomic programs in exchange for an end to nuclear-related sanctions, which resume next week in Vienna.

But Washington says a successful investigation by IAEA must be part of any final deal. That is unlikely by Nov. 24 — the target date for such an agreement.

Two diplomats from IAEA member nations who spoke to The Associated Press demanded anonymity because their information is confidential. They said the U.S. expert first applied for a visa eight months ago and had been turned down several times since.

Iran says it doesn't want nuclear arms and never worked toward them. But the agency says it has collected about 1,000 pages of information that point to attempts to develop such weapons.

Several meetings have resulted in little progress since Iran and the IAEA agreed late last year on a new effort to try and clear up the allegations.

The agency said Thursday that Iran presented no new proposals at the latest talks with IAEA experts. An IAEA statement gave no date for a new meeting.