Iran began enriching uranium to 60 per cent purity to demonstrate its technical ability after a sabotage attack on a nuclear plant to the south of Tehran, but the measure can be reversed if the US lifts sanctions, the Iranian government said on Tuesday.
Talks in Austria to take the US and Iran back to full compliance with a 2015 nuclear deal were complicated by an explosion at Iran's main uranium enrichment facility at Natanz.
Iran responded by saying it was enriching uranium to 60 per cent fissile purity, a big step towards weapons grade from the 20 per cent it achieved some time ago.
The 2015 pact between Iran and six world powers capped purity at 3.67 per cent for Iran - suitable for generating civilian nuclear energy. The regime denies seeking an atomic weapon.
"The start of 60 per cent enrichment in Natanz was a demonstration of our technical ability to respond to terrorist sabotage at these facilities," Iranian government spokesman Ali Rabiei told reporters in Tehran.
"This measure can quickly be reversed for a return to the agreed enrichment level in the nuclear accord if other parties commit to their obligations," Mr Rabiei said in remarks streamed live on a state-run website.
Tehran said the Natanz explosion was an act of sabotage by Israel, and on Saturday Iranian authorities named a suspect.
Israel has not formally commented on the incident.
Iran and world powers have made some progress on how to revive the 2015 accord abandoned by the US in 2018.
An interim deal could be a way to a lasting settlement, Iranian officials said on Monday.
In Jerusalem, Israeli Foreign Minister Gabi Ashkenazi told visiting British Cabinet Office Minister Michel Gove that Iran should not be permitted to obtain a nuclear weapon.
"Iran is undermining stability in the entire Middle East, and the international community must act to prevent Iran from achieving nuclear weapons capability. Not today and not in the future," an Israeli statement quoted Mr Ashkenazi as saying.
