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VIENNA, Austria - A senior UN nuclear inspector spoke Wednesday of a "good trip" to Tehran and the agency said his team will return to Iran's capital in late February, indicating progress on attempts to investigate suspicions that Iran is secretly working on nuclear weapons.

The International Atomic Energy Agency's announcement of a renewed mission to Tehran Feb. 21 came just hours after the return of a senior team and word from the team leader that a new trip was planned "in the very near future."

Neither the IAEA's formal statement nor mission Head Herman Nackaerts gave details on what the agency's experts had achieved. But any headway would be significant after more than three years of Iranian stonewalling on attempts to investigate the allegations.

Nackaerts spoke of "three days of intensive discussions," telling reporters at Vienna airport that -- while "there still is a lot of work to be done" -- the IAEA is "committed to resolve all the outstanding issues, and the Iranians said they are committed too."

Asked how the visit was, he replied, "we had a good trip."

Like Nackaerts, the IAEA statement also suggested some progress by indicating that the Iranian side did not reject the agency's requests out of hand, as it has in the past on the issue of weapons work. It said the agency team "explained its concerns and identified its priorities, which focus on the clarification of possible military dimensions to Iran's nuclear program."

"The IAEA also discussed with Iran the topics and initial steps to be taken, as well as associated modalities," said the statement, citing IAEA chief Yukiya Amano as saying "it remains essential to make progress."

The visit, it said, will last for two days.

Diplomats familiar with IAEA strategy told The Associated Press before the trip that the agency delegation was unlikely to settle for vague promises or complicated plans that could further stall their probe.

Any progress on the issue would be significant, at a time of growing tensions over fears that Iran might be using the cover of a peaceful nuclear program to move to the point where it can break out into making a bomb -- and growing concerns that Israel could be planning a pre-emptive attack.

Alluding to such fears, UN Secretary-General Ban Ki-moon on Wednesday told Israel that the international standoff over Iran's suspect nuclear program must be resolved peacefully.

At a news conference with Israel's prime minister in Jerusalem, Ban urged the Iranians to prove their nuclear program is for peaceful purposes. When asked whether he fears an Israeli attack, he said "there is no alternative to a peaceful resolution of these issues."

While Iran has publicly belittled efforts to force it to compromise on its nuclear programs, sanctions and other international pressure appear to have left their mark, as reflected by the indications that the IAEA mission made some progress.

Beyond that, Tehran has in recent weeks repeatedly said it is willing to enter new talks with the six world powers that have taken the lead in attempts to nudge Iran into nuclear concessions.

Iranian Foreign Minister Ali Akbar Salehi repeated such readiness Wednesday, saying Tehran hopes such "upcoming talks ... will be held in the not too distant future."

Iran has refused to discuss the alleged weapons experiments for more than three years, saying they are based on "fabricated documents" provided by a "few arrogant countries" -- a phrase authorities in Iran often use to refer to the U.S. and its allies.

Faced with Iranian stonewalling, the IAEA summarized its body of information in November in a 13-page document drawing on 1,000 pages of intelligence. It stated then for the first time that some of the alleged experiments can have no other purpose than developing nuclear weapons.

The IAEA team was seeking progress on its efforts to talk to key Iranian scientists suspected of working on a weapons program. They also hoped to break down opposition to their plans to inspect documents related to nuclear work and secure commitments from Iranian authorities to allow future visits.

Beyond concerns about the purported weapons work, Washington and its allies want Iran to halt uranium enrichment, which they believe could eventually lead to weapons-grade material and the production of nuclear weapons. Iran says its program is for peaceful purposes -- generating electricity and producing medical radioisotopes to treat cancer patients.

Since the discovery in 2002 that Iran was secretly working on uranium enrichment, the nation has expanded that operation to the point where it has thousands of centrifuges churning out enriched material -- the potential source of both nuclear fuel and fissile warhead material.

Iran also has started producing uranium at a higher level than its main stockpile -- a move that would jump start the creation of highly enriched, weapons grade uranium, should it chose to go that route. And it is moving its higher-enriched operation into an underground bunker that it says is safe from attack.

Tehran is under four sets of UN Security Council sanctions because of its refusal to heed international concerns about its nuclear programs, as well as penalties imposed by the United States and Western nations meant to force it into dialogue.

The European Union last week imposed an oil embargo on Iran and froze the assets of its central bank. In December, the U.S. said it would bar financial institutions from the U.S. market if they do business with Iran's central bank.