Washington ? Iran has reinstated an offer for U.N. nuclear agency officials to visit Tehran, but is not saying whether they will be able to focus on suspicions that it is secretly working on nuclear arms — a key condition set by the agency, diplomats said Monday.

The renewed invitation to the International Atomic Energy Agency comes after a previous offer was withdrawn. It appears to reflect Iranian efforts to deflect pressure over mounting allegations that Iran is experimenting with components of a nuclear weapons program.

A senior diplomat — one of four who agreed to discuss the confidential issue only on condition of anonymity — said a top-level IAEA mission could fly to Tehran in late January.

But he told The Associated Press that would only be likely to happen if Tehran agrees to meet IAEA calls to supply information on its alleged secret weapons work. He added that a Dec. 14 letter from Iran to agency chief Yukiya Amano offered no such specifics beyond saying that such a trip could take place.

Amano had already turned down an invitation to visit earlier this year, suggesting the trip would serve no purpose unless Iran agreed to discuss direct agency concerns, including the alleged work on nuclear arms.

Detailing such purported efforts in a 13-page summary issued Nov. 8, the IAEA concluded that “while some of the activities … have civilian as well as military applications, others are specific to nuclear weapons.”

Among these were indications that Iran has conducted high explosives testing and detonator development to set off a nuclear charge, as well as computer modeling of a core of a nuclear warhead. The report also cited preparatory work for a nuclear weapons test, and development of a nuclear payload for Iran’s Shahab 3 intermediate range missile — a weapon that can reach Israel, Iran’s arch foe.

Any mission would likely be headed by top IAEA investigator Herman Nackaerts. Iran had already invited Nackaerts for talks “aiming at a resolution of matters” ahead of his agency’s report.

But after circulation of the IAEA report to the agency’s 35 board members and the U.N. Security Council, Ail Asghar Soltanieh, Iran’s IAEA delegate abruptly announced that the trip was postponed, if not canceled.

He blamed the IAEA, saying it had “messed up” the trip by publishing its report.

The diplomats said Soltanieh had signed Dec. 14 letter renewing the invitation. Asked to comment, Soltanieh told the AP to call back later in the week.

Beyond international concerns about its alleged secret experiments, Iran is under U.N. sanctions for refusing to stop uranium enrichment — which can produce both nuclear fuel and fissile warhead material.

Tehran insists its activities are meant to be used only for energy or research. But after some initial cooperation since U.S. and other intelligence allegations of secret nuclear arms work surfaced six years ago, it has stonewalled further IAEA attempts to probe such suspicions.

An official from an IAEA member nation told the AP that — as part of recent efforts to block the investigation — Iran is drawing up a list of scientists working on its nuclear program that will be off limits to any questioning from IAEA experts.

It named one of them as Seyed Asghar Hashemi-Tabar, describing him as the head of the detonation group in the Iranian defense ministry. But the senior diplomat said the IAEA had another name listed in that position, adding Hashemi-Tabar was not a name the agency had come across.

Iran has amassed enough enriched uranium to produce several nuclear warheads, should it choose to do so. That — and its refusal to discuss its alleged clandestine weapons-related experiments — have increased concerns that time many be running out for a diplomatic solution to the conflict.

A further concern is a military assault from Israel. Before the release of the Nov. 8 report, the country’s Defense Minister Ehud Barak warned of a possible Israeli military strike against Iran’s nuclear program, telling Israeli radio: “We continue to recommend to our friends in the world and to ourselves, not to take any option off the table.”

That phrase is often used by Israeli politicians to mean a military assault. Israeli leaders have engaged in increased saber rattling recently, suggesting that an attack was likely a more effective way to stop Iran’s nuclear program than continued diplomacy.

In a letter to President Barack Obama, 15 former senior U.S. administration officials, Western diplomats and nonproliferation experts urged Washington to increase such diplomatic efforts, warning that the alternative is a “disastrous military confrontation.”

“International pressure on Iran is now at an all time high,” read the letter, shared with the AP before publication on the website of the Washington-based non-governmental Arms Control Association. “Iran’s nuclear program is struggling to overcome technical problems.

“The time available must be used to convince Iran’s current and future leaders they stand to gain more from forgoing nuclear weapons than from any decision to build them.”