Iran has been warned it could face diplomatic or economic sanctions if it breaches the terms of its nuclear deal.
Tehran has indicated it will break the uranium stockpile limit set by the deal in the next 10 days.
Downing Street said “all options” would be examined if Iran breached the terms of the Joint Comprehensive Plan of Action (JCPOA) deal.
The deal has looked increasingly unstable since Donald Trump pulled the United States out of it.
The latest development comes at a time of heightened tension in the region following the attacks on two oil tankers, which the US and UK have blamed on Iran’s military.
Behrouz Kamalvandi, a spokesman for Iran’s atomic agency, said the country needed to increase uranium enrichment levels up to 20% – only one step away from weapons-grade material.
In response, the Prime Minister’s official spokesman said: “We have been clear about our concern at Iranian plans to reduce compliance with the JCPOA.
“Should Iran cease meeting its nuclear commitments, we would then look at all options available to us.”
Foreign Secretary Jeremy Hunt has warned there is a “great risk” of a drift to war due to Iran’s activities in the region following the attacks last week in the Gulf on two oil tankers.
Tehran has strongly denied being responsible for the attacks, but Downing Street said it was “almost certain” Iran was to blame.
I condemn yesterday’s attacks on vessels in the Gulf of Oman. UK’s assessment concludes that responsibility for the attacks almost certainly lies with Iran. These latest attacks build on a pattern of destabilising Iranian behaviour and pose a serious danger to the region
— Jeremy Hunt (@Jeremy_Hunt) June 14, 2019
The Americans have accused Iran of using limpet mines to target the tankers, pointing to video footage said to show Iranian Revolutionary Guard troops removing an unexploded mine from one of the vessels.
In recent weeks, the US has sent an aircraft carrier strike group and other military assets to the region in what the military says is defensive posturing aimed at Iranian deterrence.
The UK also has a military presence in the Gulf, although in response to reports of Royal Marines heading to the region officials stressed this was a pre-planned training exercise rather than a response to Tehran.
Officials have been meeting in Whitehall to consider the tensions in the region following the attacks on two oil tankers last week.
The Prime Minister’s official spokesman said the UK position remained that it was “almost certain that the Iranian Revolutionary Guard corps attacked the two tankers”.
“No other state or non-state actor could plausibly have been responsible,” the spokesman said.
“These latest attacks build on a pattern of destabilising Iranian behaviour and pose a serious danger to the region.
“That is why we have called on Iran to cease all forms of destabilising activity.”
The spokesman said there was “recent precedent for attacks by Iran against oil tankers” but stressed “the UK remains in close co-ordination with our international partners to find diplomatic solutions to de-escalate tensions”.
He added: “Unintended escalation would not be in any party’s interests.”
The UK had “a number of military assets in the region, including at our new naval base in Bahrain and our facility in Oman”.