Iran is working on advanced uranium centrifuges at new underground sites being built near its Natanz nuclear plant, Israel's defense minister said on Tuesday.

Benney Gantz in a speech at Reichman University near Tel Aviv gave figures that appeared to go beyond those published by the UN‘s International Atomic Energy Agency, IAEA.

Centrifuges are used to purify uranium for civilian projects or, at higher levels, to make fissile materiál for a nuclear bomb. Iranian progress in the field is being watched by world powers trying to resurrect the 2015 nuclear deal with Tehran, known as JCPOA.

"Iran is making an effort to complete the manufacturing and installation of 1,000 additional advanced IR6 centrifuges in its nuclear facilities, including new facilities being built at underground sites abutting Natanz," Gantz said.

A March 3 report by the UN International Atomic Energy Agency (IAEA) said Iran had installed or planned to install a total of three IR6 cascades, amounting to around 660 machines.

IAEA chief Rafael Grossi said last month that Iran had set up a new underground Natanz workshop for making centrifuge parts, an apparent precaution against attacks.

In his remarks, Gantz alluded to Israel's long-standing threat to take military action if it deems diplomacy is at a dead end to deny its arch-enemy the means to make nuclear weapons.

"The cost of such a future war, which we hope will not happen, can be prevented or reduced" with tougher negotiations by world powers, he said.

Reporting by Reuters