Story highlights Iran's ambassador reiterated Thursday that his country "is ready to re-engage with IAEA"

The group is concerned about enrichment activities at Fordow and Natanz

The five permanent members of the U.N. Security Council and Germany agree to talks

Irans parliament speaker warns the talks will fail if the West pressures Iran

Faced with mounting pressure from world powers over its controversial nuclear program, Iran's ambassador to the International Atomic Energy Agency reiterated Thursday that his country "is ready to re-engage with (the) IAEA."

"A new chapter is open," Ali Asghar Soltanieh told reporters at the IAEA board of governors meeting in Vienna, Austria, though has insisted a wider agreement on a range of issues must first be reached between Iran and the United Nations before nuclear inspections can begin.

Soltanieh also said his country "will never ever suspend our nuclear activities," insisting that the program is exclusively for peaceful purposes.

The ambassador's statement came shortly after six world powers called on Iran Thursday to resume nuclear talks without preconditions, urging it to grant inspectors access to its Parchin military base where satellite images have raised suspicion after they revealed apparent changes to the facility.

Soltanieh told reporters that suspicions regarding the development of nuclear weapons at Parchin were "childish" and "ridiculous."

Iran recently signaled a willingness to let U.N. inspectors visit the base, a move that could possibly ratchet down rising tensions in the region.

"We reaffirm that our overall goal remains a comprehensive negotiated, long-term solution," Germany and the five permanent members of the U.N. Security Council -- China, France, Russia, Great Britain and the United States -- said in a statement Thursday.

The nations -- collectively known as the P5 plus 1 -- expressed regret about uranium enrichment activities at the Fordow and Natanz facilities. Iran confirmed this year that it began the enrichment of uranium at its underground Fordow facility, and reports emerged last month that new advanced centrifuges were being used at Natanz.

Israel, the United States and other countries have long suspected Iran is trying to build nuclear weapons, and international inspectors have voiced concern about the possibility.

Robert Wood, acting U.S. envoy to the IAEA, said Thursday the United States will "not sit idle" while Iran "openly flouts its obligations and embarks on a path of deception and deceit."

On Wednesday, two Western diplomats told CNN that satellite images show trucks and earth-moving vehicles at the Parchin military base. The description buttresses IAEA concerns that the Iranians were trying to clean up the facility to cover signs of nuclear activity, though the images do not provide clear evidence of that claim, authorities said.

In a recent report, the U.N. agency said experiments with a nuclear detonation system had been conducted inside a large metal container at Parchin. IAEA inspectors visited the facility twice in 2005, but inspectors did not enter the building that housed the test chamber.

The P5-plus-1 countries are seeking assurances about the nature of Iran's program "while respecting Iran's right to the peaceful use of nuclear energy," Catherine Ashton, the European Union's foreign policy chief, said in a letter this week.

Ashton was responding to an overture made last month by Iranian nuclear negotiator Saeed Jalili, and it came at the same time Iran said it would grant U.N. inspectors access to Parchin.

But at an economic summit in Iran, the nation's parliament speaker, Ali Larijani, accused the West of applying a double standard: Pressuring Iran but saying nothing about Israel's nuclear capabilities, according to state media.

Israel, believed to be the only country in the region with nuclear weapon capabilities, appeared measured in its response to news of renewed talks.

Yaakov Amidror, the Israeli national security chief, said Israel welcomed the talks but warned that "we must be ready for the possibility the talks will fail."

In an interview Wednesday on Kol Yisrael, Amidror said that without a military option to back up the talks, he did not believe the Iranians would be willing to compromise in negotiations.

No date or location for the renewed talks has been announced.

Iran's economy has been hit hard by U.S. and European oil and financial sanctions over its nuclear activities, while another round of sanctions targeted the crude sales that make up about half of Tehran's revenue.

Israel has threatened to attack Iran's nuclear sites should peaceful alternatives be exhausted, with Netanyahu reiterating this week that Israel reserved the right to defend itself from the threat of a nuclear-armed Iran.

Iran, meanwhile, has threatened to cut off the Strait of Hormuz -- the only shipping lane out of the oil-rich Persian Gulf -- if it is attacked.

Ambassador Soltanieh said Thursday that international sanctions and cyberattacks against Iran will not prevent it from developing nuclear energy, and that sanctions were only working to hurt its citizens.

The continued Israeli threat of attack against Iran's nuclear installations, he noted, is against international law, and called on the United Nations to condemn and take action against Israel.

"We are facing a barbaric phenomenon," Soltanieh said, referring to the killing of Iranian nuclear scientists, which Iran blames on Israel.

As late as Wednesday, the IAEA director general said there were indications that Iran was engaged in the development of nuclear weapons.

"Iran is not telling us everything. That is my impression. We are asking Iran to engage with us proactively, and Iran has a case to answer," said Yukiya Amano.

He told CNN that Iran has declared a number of nuclear facilities to the IAEA, which has them under its safeguards.

"For these facilities and activities, I can tell that they are in peaceful purpose," Amano said.