The satellite image shows large pink tarpaulins pulled across two buildings. Close by, it appears that topsoil has been moved and a security fence taken down. The image, taken earlier this week and provided to CNN by DigitalGlobe, is of an Iranian military facility at Parchin, one widely suspected by Western diplomats as a secret part of the country's nuclear program.

It's one of several developments on Iran's nuclear program that worry experts -- others being: the failure of another round of talks between the International Atomic Energy Agency (IAEA) and Iranian officials; reports that Iran has increased the number of centrifuges enriching uranium; and a drumbeat of warnings from Israel that diplomacy and sanctions aren't working.

Inspectors from the IAEA have been repeatedly denied access to Parchin, some 30 kilometers (19 miles) from Tehran, so exactly what is going on there is a matter of debate.

David Albright of the Institute for Science and International Security says of the latest images: "The purpose of covering the buildings could be to conceal further cleanup activity. ... Depending on how effective of a seal the tarp provides, the goal could be continue sanitizing the inside and outside of the building that is suspected to contain particles indicative of nuclear weapons development work."

Many Western diplomats and nuclear experts believe the facility has been used to test high-explosive nuclear triggers, an essential step toward achieving a weapons capability. Iran denies that Parchin has any role in its nuclear program, which it insists is for peaceful purposes. But the satellite imagery suggests a lot of "cleaning up" has been done there.

A meeting in Vienna Friday between IAEA officials and an Iranian delegation, which in part was to discuss access to the Parchin site, ended without progress.

"The discussions today were intensive but important differences remain between Iran and the U.N. that prevented agreement," the agency's chief inspector, Herman Nackaerts, said afterwards. Friday's unsuccessful talks follow a similarly fruitless session in June, when Iran refused to allow questions about weaponization and procurement, according to sources familiar with the talks.

However, Iran openly acknowledges that it is increasing the number of centrifuges it has to enrich uranium. President Mahmoud Ahmadinejad boasted last month that 11,000 centrifuges were now operational, about 1,000 more than estimated by the IAEA in May.

Diplomats in Vienna say a new IAEA report due next week will confirm that additional centrifuges have been installed at the Fordow (near Qom) underground site - the most difficult facility to attack because it is deep inside a mountain. It's not clear whether those additional centrifuges are all fully installed or operational. Details of the forthcoming IAEA findings were first reported by Reuters.

The combination of ongoing suspicion about Parchin and the further expansion of the centrifuge program is likely only to reinforce Israel's lack of faith in diplomacy and an ever-growing raft of international sanctions as capable of reining in the Islamic Republic's nuclear program. Israeli Prime Minister Benjamin Netanyahu said Friday that the new centrifuges were "proof that Iran is continuing accelerated progress towards achieving nuclear weapons and is totally ignoring international demands."

A senior U.S. official told CNN: "The numbers of centrifuges being installed and operating will add to Iran's ability to produce more 20% low-enriched uranium. The fact that they will be operating at Qom is also problematic, given that it is an underground facility."

But the official added: "In the overall scale of Iran's enrichment program, the numbers of new machines do not change significantly the amount of time Iran would need to break out."

"Iran has over 9,000 centrifuges installed and operating at Natanz and probably has added a few hundred at Qom."

David Albright - who has long followed Iran's program -- says the key is the amount of 20% enriched uranium being produced. It is far more than required for the Tehran research reactor, he says, and the increased rate of production suggests that by early next year, Iran will have enough uranium of 20% purity to begin enriching sufficient weapons-grade uranium (80 or 90%) for a nuclear device.

"We don't know how fast Iran can break out," Albright told CNN - referring to the window it would need to produce enough highly enriched uranium (HEU) for a weapon. "But by early next year it may be just one month, and it used to be six months, so that is the most troubling development."

"We just don't know their thinking. Maybe they would continue to accumulate 20% uranium," he said.

Albright said there was an emerging consensus that even if it did produce weapons-grade uranium, Iran would still need several months to make a crude nuclear device, and longer still to make a deliverable warhead.

"It may be they will try to follow the North Korean model -- to test a crude device underground so as to cross the nuclear threshold," he said.

Both the United States and Israel have said that a nuclear-armed Iran would be unacceptable. And the Israelis believe that Iran has made progress towards a deliverable warhead.

Israel's intentions remain the focus of fevered speculation, with some former Israeli officials suggesting that the security cabinet could green-light a strike against Iran's nuclear facilities within months.

Senior ministers have done nothing to temper the speculation. Defense Minister Ehud Barak told a graduation ceremony at the National Security College last month: "I am well aware of the difficulties and complexities involved in stopping Iran from obtaining nuclear weapons, but it is abundantly clear to me that dealing with the (alternative) situation when it unfolds would be substantially more complex, more dangerous and more costly both to lives and resources."

Israel's calculations are fundamentally different from those of the United States. Were it to strike Iran's nuclear program, its air power would be stretched to the limit. With its planes overflying hundreds of miles of hostile territory and requiring midair refueling, Israel would be limited to a "one-shot campaign." Intelligence analysts believe that only the United States could sustain a campaign capable of terminal damage to the Iranian program.

Dov Zakheim, former under secretary of defense in the Bush administration, follows the evolving crisis closely.

"Israeli leaders know that the most they can do is shut down Iran's nuclear program for two or three years at the outside," he says.

"The political leaders are being told the same things as Begin was told before Israel attacked (the Iraqi reactor at) Osirek in 1981 -- but he still went ahead," Zakheim told CNN.