Foreign Secretary Jeremy Hunt says there is a "small window" to save the Iran nuclear deal, as he launches a fresh bid to ease tensions in the Persian Gulf.
Mr Hunt is meeting EU foreign ministers in Brussels to raise concerns about Iran breaching some of its commitments.
The deal, which involves Iran limiting nuclear activities in return for the easing of economic sanctions, is under pressure after the US withdrew in 2018.
The summit comes amid heightened tensions between the UK and Iran.
The UK seized an Iranian oil tanker earlier this month and, in response, Iran threatened to detain a British oil tanker.
However, Hunt said on Saturday the tanker could be released if the UK is guaranteed the oil it was carrying is not bound for Syria.
Speaking on his way into the meeting, Hunt said the Iran nuclear deal was not dead "yet", but he warned that if Iran acquired nuclear weapons it would become "a very, very toxic and dangerous situation".
He added: "Iran is still a good year away from developing a nuclear weapon. We think there is still a cosing, but small, window to keep the deal alive."
He Hunt is working with the European partners of the deal - France and Germany - to find a way to "preserve" the agreement.
In a joint statement issued ahead of the meeting, Britain, France and Germany reiterated their support for the deal.
But said they were "deeply troubled" by recent events in the Persian Gulf and "concerned" over US-Iran relations.
"We believe the time has come to act responsibly and seek a path to stop the escalation of tensions and resume dialogue," the statement said.
"The risks are such that it is necessary for all stakeholders to pause and consider the possible consequences of their actions."
Earlier this month Iran said it would be breaching the deal by breaking a limit set on uranium enrichment.