TEHRAN, Iran (AP) — Celebrating a holiday marking when Iran first enriched uranium, the Islamic Republic’s Supreme Leader urged negotiators Wednesday not to give into “coercive words” in talks with world powers over the country’s contested nuclear program.

Ayatollah Ali Khamenei, who has the final say on all state matters, remained defiant in the speech given on Iran’s National Day of Nuclear Technology, saying its program will continue.

“Our negotiators should not accept any coercive words from the other party,” Khamenei told Iranian nuclear scientists at a commemoration. “None of the country’s nuclear achievements can’t be stopped and no one has the right to bargain over it.”

The holiday comes as Iranian negotiators met Wednesday in Vienna with representatives from Britain, China, France, Germany, Russia and the US in Vienna to continue their talks, which have shown little progress. The next round is already set for May, also in Vienna.

A first-step deal with world powers, in effect since January, has curbed some Iranian nuclear activities in return for limited sanctions relief as the two sides work toward a final agreement. Negotiators face an informal July deadline to come up with a permanent deal.

The West accuses Iran of trying to build atomic weapons with its nuclear program. Iran says its program is for peaceful purposes, like power generation and medical research. The Islamic Republic argues it needs robust enrichment capacities in order to make low-enriched reactor fuel.

Khamenei said Wednesday that Iran agreed to talks with world powers to show it wasn’t seeking nuclear weapons.

“It was agreed to hold talks to break the hostile atmosphere,” he said. “These talks need to continue but all must know that despite continuation of the talks, activities of the Islamic Republic of Iran in the field of nuclear research and development won’t be halted at all. Nuclear achievements are unstoppable.”

The US, Britain, France and Germany want significant cuts to limit the potential for Iran’s program to be used for making high-enriched material for nuclear arms. Russia and China are somewhere in the middle.

The six also want to eliminate potential proliferation dangers from an enrichment site at Fordo, south of Tehran, that is built far underground to withstand air strikes. They want the same for a nearly built nuclear reactor at Arak, in central Iran, that would produce substantial amounts of plutonium. Like enriched uranium, plutonium can be used for the core of a nuclear weapon.

Times of Israel staff contributed to this report.