The European powers party to the Iran nuclear deal told Tehran on Wednesday that its decision to enrich uranium at 60-percent purity and install a further 1,000 centrifuges at its Natanz site were contrary to efforts to revive the 2015 nuclear deal.
Talks between world powers, Iran and the United States are due to resume in Vienna on Thursday, but in a joint statement Britain, France and Germany said Tehran's decision to enrich at 60 percent was not based on credible civilian reasons and constituted an important step in the production of a nuclear weapon.
"Iran's announcements are particularly regrettable given they come at a time when all JCPoA (Joint Comprehensive Plan of Action) participants and the United States have started substantive discussions, with the objective of finding a rapid diplomatic solution to revitalise and restore the JCPoA," the three countries said.
"Iran's dangerous recent communication is contrary to the constructive spirit and good faith of these discussions."
Tehran has said its decisions came after arch-foe Israel sabotaged its key Natanz nuclear site on Sunday.
"In light of recent developments, we reject all escalatory measures by any actor, and we call upon Iran not to further complicate the diplomatic process," the E3 said.
Also on Wednesday, Saudi Arabia said it was concerned about Iran's intention to start 60-percent enrichment and said such a move could not be considered part of a peaceful nuclear program.
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A Foreign Ministry statement on state media called on Iran to avoid escalation and engage seriously in current talks with global powers, while urging the international community to reach an agreement "with stronger parameters of a longer duration".
They added that any deal should "also take into consideration the deep concern of regional states over escalatory steps by Iran to destabilise regional security and stability, including its nuclear program."
Saudi Arabia and Iran have been locked in several proxy wars in the region, including in Yemen where the Iran-aligned Houthi movement has launched cross-border missile and drone attacks at the kingdom.
After an explosion at its Natanz uranium enrichment site on Sunday blamed by Tehran on arch-foe Israel, Iran said it would begin enriching uranium at 60 percent, a move bringing the fissile material closer to levels suitable for a bomb.
President Hassan Rohani reiterated earlier on Wednesday in a televised cabinet meeting Tehran's claim Israel may be behind the Natanz attack. "Of course, the security and intelligence officials must give the final reports, but apparently it is the crime of the Zionists, and if the Zionists act against our nation, we will answer it," he said .
"Our response to their malice is replacing the damaged centrifuges with more advanced ones and ramping up the enrichment to 60 percent at the Natanz facility."
Iranian authorities have described the incident as an act of "nuclear terrorism".
Israel, which the Islamic Republic does not recognise, has not formally commented on the matter.
The International Atomic Energy Agency, the UN nuclear watchdog, said on Tuesday it had been informed of Iran's decision.
Iran's 2015 nuclear deal, which it has been breaching since the United States withdrew in 2018 and reimposed sanctions on Tehran, caps the fissile purity to which Tehran can refine uranium at 3.67 percent.
That is well under the 20 percent achieved before the agreement and far below the 90 percent suitable for a nuclear weapon.
In an apparent bid to heap pressure on U.S. President Joe Biden's administration that is willing to revive the accord, Iran in recent months has raised enrichment to 20-percent purity, a level where uranium is considered to be highly enriched.
Rouhani, echoing Iran's stance for decades, said Tehran had no intention to obtain or develop nuclear weapons.
Last week, Iran and the global powers held what they described as "constructive" talks to salvage the 2015 accord.
"They (Israel) want our hands to be empty in the negotiations, but we will be in the negotiations with a stronger hand," Rohani said.