In a letter to the UN Security Council seen Thursday by AFP, these three countries known as the E3 say they "remain committed to a diplomatic solution to the Iran nuclear issue."

"We reiterate our determination to use all diplomatic tools to prevent Iran from acquiring a nuclear weapon, including using snapback if necessary," they added.

This term alludes to a mechanism in a landmark 2015 deal on Iran's nuclear program that allows signatories to reimpose sanctions which had been eased.

That deal with Tehran traded sanctions relief for limits on its nuclear program.

It was signed by Iran on one side and France, Germany, Britain, China, Russia and the United States on the other.

But in 2018 then US president Donald Trump pulled the United States out of the agreement and reimposed US sanctions against Iran.

Iran has retaliated by increasing its production of uranium enriched to 60 percent -- on its way to the 90 percent needed to make a nuclear weapon.

"We are rapidly approaching a critical juncture on UNSCR 2231 next year. Iran must deescalate its nuclear program to create the political environment conducive to meaningful progress and a negotiated solution," the European letter said.

That resolution endorses the 2015 agreement with Iran and expires in October 2025, 10 years after the accord went into effect.

The Security Council is scheduled to address the Iranian nuclear issue next week.

Representatives of the E3 and Iran met in Geneva last month and agreed to keep talking.

Iran says it has the right to nuclear energy for peaceful purposes and has consistently denied any ambition of developing weapons capability.