VIENNA, Austria -- International officials pursued a two-pronged effort Wednesday to engage Iran over concerns the country may have worked on nuclear weapons, with a U.N. team seeking access to a site linked to such suspected activity and European Union negotiators looking to restart talks with Tehran meant to ease such fears.

Preparing to depart Vienna for Tehran, Herman Nackaerts of the International Atomic Energy Agency signalled impatience with Iran's refusal to meet IAEA requests for information on its suspicion that the Islamic republic had researched and developed components of a nuclear weapons program. In brief comments, he noted "negotiations for almost one year" have already been conducted on the issue.

Nackaerts, who heads the IAEA's nuclear investigation, also told reporters his team was "ready to go" to Parchin, an Iranian site it suspects could have been used for such experiments, just as soon as Tehran approves a visit. In Tehran, he will push IAEA requests for access to information, officials and locations the agency thinks may have been used for weapons work.

Iran says it does not want atomic arms and justifies delays in co-operating with the IAEA by saying that a framework regulating the agency's probe must be agreed on first. But as the negotiations on such an agreement drag on, agency officials have complained that it is nothing more than a delaying tactic. They are particularly concerned that such delays can hurt their efforts to investigate Parchin.

The IAEA suspects that Iran has conducted live tests of conventional explosives there that could be used to detonate a nuclear weapon and cites satellite photos indicating a cleanup of the site at a sprawling military base southeast of Tehran. Iran denies it is sanitizing the site, but IAEA chief Yukiya Amano has warned that his agency's chances of a meaningful investigation at Parchin are diminishing the longer the alleged cleanup continues.

Emailing a series of commercial satellite photographs to The Associated Press Wednesday, the Institute for Science and International Security said the images showed "a steady pace of what appears to be the 'reconstruction' phase of the site, which between April and July 2012 had undergone considerable alterations.

"Such alterations included building demolitions and earth displacement," said ISIS, whose head, David Albright, frequently briefs U.S. government branches on Iran's nuclear program. "The latest imagery from December 9, 2012 shows what appears to be a new, almost completed security perimeter around the site.

"A new site layout is taking shape and the presence of dirt piles and a considerable number of earth moving vehicles and cars suggest that construction is continuing at a steady pace."

In a separate email to the AP, nuclear scientist Yousaf Butt questioned the significance of the images.

"I don't see a problem with Iran making a fence around a military base," wrote Butt, who has challenged the legality of some of the IAEA's Iran investigation attempts and is skeptical of allegations that Iran may be working on nuclear arms.

Noting the IAEA suspicions at Parchin focus on non-nuclear explosives, Butt wrote that "the IAEA's legal authority to pursue allegations of conventional explosives work is limited by international law."

The international community is also concerned about Iran's uranium enrichment -- a program Tehran says is geared only toward making reactor fuel. But enrichment can also create the core material of nuclear weapons.

While developing nations insist Iran has a right to enrichment, Western governments and Israel fear it could be a cover for weapons aspirations -- concerns fed by Iran's decision to boost enrichment grades last year to a level that is only a technical step short of weapons-grade uranium.

Six world powers have in recent months been developing a new approach to persuade Iran to curb at least higher-level enrichment. These include the possible easing of international sanctions crippling Tehran's oil sales and financial dealings, if it compromises.

In Brussels, an EU official said that Helga Schmid, deputy director of the European Union's diplomatic corps, spoke on the phone with Ali Bagheri, Iran's deputy nuclear negotiator, to discuss dates and venues for a new meeting with Iranian negotiators.

The official said the six countries negotiating with Iran remain united in seeking a diplomatic solution to the nuclear issue. The countries are France, Germany, Britain, China, Russia and the U.S. The official spoke on condition of anonymity because he was not authorized to discuss the matter.

In Tehran, Iranian President Mahmoud Ahmadinejad said Wednesday he had already announced back in 2007 that Iran had "become nuclear" by mastering all aspects of peaceful atomic technology.

"Efforts to prevent Iran from achieving this capability are (thus) irrelevant," he said in comments on his website that appeared to allude to the six powers' diplomatic efforts. "So, it's better to co-operate and work together."