TEHRAN: Iran’s supreme leader warned Wednesday against protracted talks on the country’s atomic programme, in remarks on the eve of another round of negotiations aimed at reviving a landmark nuclear accord.

Tehran declared Tuesday it will sharply ramp up its enrichment of uranium, two days after what it says was an act of Israeli “nuclear terrorism” against its enrichment plant in Natanz.

The announcement has cast a shadow over talks in Vienna aimed at salvaging the 2015 nuclear deal between Iran and world powers that then US president Donald Trump abandoned almost three years ago.

“We have to be careful” that the dialogue is not conducted “in a way that parties drag (out) the negotiations, as that is harmful for the country,” Ayatollah Ali Khamenei said in remarks broadcast by state television on Wednesday.

The supreme leader also warned that Iran had to be wary of the Americans during the negotiations.

The Islamic republic had earlier in the day said its decision to boost uranium enrichment to 60 percent purity was a response to arch-foe Israel’s “nuclear terrorism” against the Natanz facility, where an explosion knocked out power on Sunday.

Iran’s enrichment move brings it a step closer to the 90 percent threshold for military use and shortens its “breakout time” to build an atomic bomb.

Under the nuclear deal formally known as the Joint Comprehensive Plan of Action, it had committed to keep enrichment to 3.67 percent, though it stepped this up to 20 percent in January.

The European parties to the accord — Britain, France and Germany — on Wednesday expressed “grave concern” over the enrichment move, while also rejecting “all escalatory measures by any actor”.