TEHRAN, Iran (AP) — A senior Iranian negotiator said late Friday nuclear talks with world powers could be extended again if no deal is reached by the November 24 deadline.

The negotiator, Deputy Foreign Minister Abbas Araqchi, was quoted by the semiofficial Fars news agency as saying that an extension was under consideration and that it was “possible.”

Araqchi said that if existing differences between Tehran and the six world powers — the five permanent members of the UN Security Council plus Germany — were not resolved in the upcoming round of talks next week in Vienna, a deal by the November deadline would not be possible.

The talks were already extended once earlier this year. They reportedly remain stuck over the size and output of Iran’s uranium enrichment program, a possible pathway to nuclear arms.

A Kuwaiti news site claimed Thursday that a foreign country was responsible for a blast at Iran’s secretive Parchin facility on Monday, quoting unnamed Washington-based European diplomats.

Screenshot from Israel Defense showing satellite images of the Parchin site east of Tehran before and after Monday's explosion at the suspected nuclear facility on October 8, 2014.

The report by Kuwait’s Al Rai also claimed Western intelligence agencies believed that Iran had been conducting tests at the facility, aimed at loading nuclear warheads onto ballistic missiles.

The blast, which is said to have killed at least two people, caused substantive damage to 12 buildings at the heart of the site, Channel 2 said Thursday.

According to satellite images taken after the blast, Israeli researcher Ronen Solomon told the TV channel, the affected buildings were bunkers where work was being carried out on triggers to detonate nuclear devices.

The reports emerged just as the latest UN effort to probe suspicions that Iran was working to attain nuclear weapons ended on a downbeat note, with diplomats saying that Tehran refused entry to Iran to a US nuclear expert on the UN’s investigating team.

The diplomats also said Thursday that the trip this week didn’t succeed in advancing a decade of UN efforts to investigate suspicions that Tehran worked on such weapons.

Tehran has denied IAEA inspectors access to Parchin since 2005.

Reza Najafi, Iran’s envoy to the IAEA, confirmed that an International Atomic Energy Agency staff member was refused a visa.

The IAEA’s inquiry is formally separate from US-led talks with Iran focused on long-term caps on Tehran’s atomic programs in exchange for an end to nuclear-related sanctions, which resume next week in Vienna.

Iran says it doesn’t want nuclear arms and never worked toward them. But the IAEA says it has collected about 1,000 pages of information that point to attempts to develop such weapons.

Several meetings have resulted in little progress since Iran and the IAEA agreed late last year on a new effort to try and clear up the allegations.

The agency said Thursday that Iran presented no new proposals at the latest talks with IAEA experts. An IAEA statement gave no date for a new meeting.

On Wednesday, an exiled Iranian opposition group accused Tehran of secretly moving a key nuclear research hierarchy to avoid international inspections.

The dissident group said the Tehran-based Organization of Defensive Innovation and Research (SPND) was “the nerve center of the militarization of the Iranian nuclear program,” which has been responsible for “the design and manufacture of the atomic bomb.”

“The transfer of the SPND was completed in July,” said the Paris-based National Council of Resistance of Iran (NCRI), which has made significant revelations about Iran’s nuclear program in the past.

“Managers and key services were relocated to secret locations, while some administrative officials were left in place to deceive IAEA inspectors,” said dissident leader Afchine Alavi.

The SPND was targeted in August by a new round of US sanctions against companies and individuals seen as providing support to illicit Iranian nuclear activities.

The brains behind the SPND, Mohsen Fakhrizadeh, sought for years by the International Atomic Energy Agency (IAEA), is being “hidden by the regime”, the NCRI said in a report.

“This game of hide-and-seek with the IAEA proves that the regime has no intention of abandoning the military aspect of its program and that it does not want to be transparent.”