Iran announced Wednesday that it had begun to install a new generation of uranium enrichment centrifuges to produce nuclear fuel at its Natanz facility.

The announcement coincided with Wednesday’s talks between Iran and senior UN nuclear inspectors seeking to expand probes into suspected weapons-related tests. It also could add pressure to planned negotiations later this month between Iran and world powers in Kazakhstan.

The official IRNA news agency quoted Iranian nuclear chief Fereidoun Abbasi as saying that Iran began installing the new, more advanced centrifuges at the Natanz site in central Iran about a month ago. He said they would only be used to produce low-level enriched uranium.

But advanced centrifuges can vastly increase Iran’s pace of enrichment, which the West fears could be eventually turned into warhead-grade material. Iran insists it wants nuclear fuel only for energy reactors and research.

Senior UN investigators were in Iran Wednesday for a new round of talks with government officials over allegations that Tehran may have carried out tests on triggers for atomic weapons.

The visit by the UN team, led by Herman Nackaerts, comes a day after Tehran raised prospects that the IAEA may be allowed to inspect Parchin — a military site where the agency suspects nuclear-related experiments were conducted — if certain conditions were met.

However, IAEA director general Yukiya Amano said on Monday that “the outlook is not bright” for a Parchin visit, according to The New York Times. Iran denies any testing activity at Parchin and insists the facility is a conventional military site only.

The possibility of Iran nuclear tests came under greater scrutiny this week, after North Korea successfully tested a nuclear device on Tuesday, setting off a wave of international condemnation. North Korea and Iran are suspected to have shared nuclear technology.