Officials from the United Nation’s nuclear watchdog were set to meet Iranian officials in Vienna Friday, though they harbored slim hopes for a breakthrough on gaining access to nuclear sites.

Adding to the pressure on International Atomic Energy Agency officials were reports that Iran is stepping up enrichment activity behind closed doors.

Going into the meeting,  Iranian envoy Ali Asghar Soltanieh told reporters both sides were trying to bridge disagreements, adding: “I hope for success.”

Senior IAEA official Herman Nackaerts was more circumspect, saying only “his team sought agreement on resolving all the outstanding issues” — terminology the agency uses for suspected nuclear weapons research and development by Iran.

On Thursday, diplomats in Vienna told Reuters that Iran had increased uranium enrichment activities at the Fordo facility, a key nuclear site buried deep underground.

The news comes less than a month after a National Intelligence Estimate out of Washington reportedly contained new information detailing a “notable” increase in enrichment activity by Tehran.

Despite talk of a breakthrough in May between the IAEA and Iran, little headway has been made. The last meeting between the parties, in June, ended in a deadlock.

At the Friday meeting, senior IAEA officials were expected to press Iranian representatives for access to a site at the Parchin military complex southeast of Tehran that they suspect was used for nuclear-weapons-linked experiments.

Tehran says a visit is possible only after extensive planning and a detailed outline of procedures. IAEA officials in turn privately describe that caveat as a stalling tactic, citing satellite photos apparently showing a major clean-up effort at the site.

Iran has repeatedly turned down IAEA requests for access and agency chief Yukiya Amano was downbeat ahead of Friday’s talks.

“I cannot say that I am optimistic about the outcome of the coming meeting,” he told reporters in Helsinki, Finland, on Wednesday. “I cannot say when we can reach agreement.”

On Thursday, Amano announced the creation of a special Iran task force drawing together sleuths in weapons technology, intelligence analysis, radiation and other fields of expertise.

Creating a unit focused on only one country is an unusual move for the International Atomic Energy Agency, reflecting the priority the UN nuclear watchdog is attaching to Iran amid fears that it is moving closer to the ability to make nuclear weapons. It also indicates frustration by top agency officials over Iran’s refusal to cooperate with IAEA experts who are trying to follow up on suspicions that Tehran was — or is — secretly working on an arms program.

Iran maintains its nuclear program is for peaceful purposes. 

On Tuesday, IAEA officials charged that Iranians were scrubbing Parchin of any trace of weaponization tests.

Earlier this year, the IAEA showed its 35 board member nations satellite images of the site that apparently showed suspicious activity. According to the diplomats who attended the closed meeting, the images showed that at least two buildings were razed and water streaming out of another structure suspected of hiding a metal chamber allegedly used to test explosives that could be used to set off a nuclear charge.

While enrichment at Parchin is currently occupying the IAEA, news of increased activity at Fordo may prove a more vexing problem. Buried deep inside a mountain, It is also surrounded by anti-aircraft batteries and other defenses run by Iran’s powerful Revolutionary Guard.

Diplomatic sources told Reuters that centrifuges were being moved into the Fordo nuclear facility south of Tehran, with one source saying hundreds of such machines had been installed at the site.

Israel, which is reportedly considering military action against Iran to end its nuclear program, would likely have a hard time destroying the Fordo facility with its current military capabilities, analysts say.

Concurrent to the talks between the IAEA and Tehran over access are negotiations over curbing the program between Iran and six worlds powers known as the P5+1. On Wednesday, Washington Post columnist David Ignatius reported that Iran had unofficially signaled willingness to cap future enrichment at five percent.

Quoting a former nuclear negotiator for Iran, Ignatius wrote that the Islamic Republic may be willing to agree to export its current stockpile of 20 percent enriched uranium and agree to a “zero stockpile” formulation, which would force the country to immediately convert any uranium into fuel rods or export it.

Israel has said it will only accept zero percent enrichment by Iran, though P5+1 negotiators are reportedly more flexible.

While talks between Iran and the P5+1 have stalled, and been frozen for the past month, EU Foreign policy chief Catherine Ashton is expected to call Iranian nuclear official Saeed Jalili sometime this month to discuss restarting negotiations.

Israel maintains that the talks are a stalling tactic, though the US and Western powers say there is still time for diplomacy to work.