LONDON 

The UK warned on Friday that time is running out to reach a diplomatic agreement with Iran on its nuclear program, as talks with European and US partners continue.

UK Foreign Secretary David Lammy said Britain remained committed to diplomacy but was prepared to pursue sanctions if no progress was made.

In a post on US social media platform X, Lammy said he had spoken by phone with Iranian Foreign Minister Seyed Abbas Araghchi and European partners to “reiterate concerns about Iran’s nuclear program.”

"We are committed to diplomacy, but time is short. We have offered Iran a diplomatic solution with an extension to sanctions relief. Without a verifiable durable deal, this will end," he said.

The UK, France and Germany -- the European parties to the 2015 nuclear deal -- as well as the EU’s foreign policy chief Kaja Kallas, also held a call with Araghchi earlier this week.

Discussions centered on the so-called “snapback” mechanism, which allows UN sanctions against Tehran to be reinstated if it is judged to be in breach of the agreement.

According to Iran’s state news agency, IRNA, those calls also covered Tehran’s position on the snapback mechanism and what responsibilities European countries hold in relation to it.

Araghchi argued that European powers had failed to uphold their commitments under the 2015 accord, and therefore lacked the “legal and moral” grounds to trigger the mechanism.

Iran and six countries -- the US, UK, France, China, Russia and Germany -- signed a landmark agreement in July 2015. It offered relief from sanctions in return for restrictions on Iran’s nuclear activities.

In 2018, the US unilaterally withdrew under President Donald Trump and reimposed sanctions on Tehran.

Iran subsequently began scaling back its commitments a year later, including stepping up uranium enrichment, after accusing European states of failing to mitigate the effect of US measures.

The European parties, known as the E3, have since threatened to invoke the snapback mechanism to restore UN sanctions, unless Iran complies. The deadline for doing so expires Oct 18.

Last month, deputy foreign ministers from Iran, the UK, France and Germany met in Istanbul and agreed to continue talks.

Tehran has warned that if the UN sanctions are restored, it may reconsider its membership of the Nuclear Non-Proliferation Treaty (NPT), which it has been a party to since 1970.