Keir Starmer has called a Cobra meeting this morning after Iran was hit by air strikes from a US and Israel coalition.
Britain has denied being part of what Trump called a "major combat operation" in the Middle East.
Downing Street issued a statement which read: “Iran must never be allowed to develop a nuclear weapon and that is why we have continually supported efforts to reach a negotiated solution.
“Our immediate priority is the safety of UK nationals in the region and we will provide them with consular assistance, available 24/7.
“As part of our longstanding commitments to the security of our allies in the Middle East, we have a range of defensive capabilities in the region, which we have recently bolstered. We stand ready to protect our interests.
“We do not want to see further escalation into a wider regional conflict.”
It comes as a senior Labour MP has said UK should not join a war.
US and Israeli forces carried out a series of strikes on Tehran and other cities on Saturday morning, claiming they were conducting a "pre-emptive" action and calling for Iranians to overthrow the regime.
Dame Emily Thornberry, chairwoman of the Commons Foreign Affairs Committee, said she had seen no indication of British involvement in the strikes and urged the Government to avoid getting involved.
She told the BBC's Today programme: "I don't think there's a legal basis for this action."
But she warned there was a risk the UK could become involved if Iran retaliated by attacking Western military bases in the region.
She said: "There's a significant permanent military presence in the Gulf, in Bahrain or Oman or UAE or Qatar, and we don't know how the Iranians are going to respond to this."
In the hours after the attack on Iran, Israeli authorities said they had detected missiles launched from Iran and warned civilians to take shelter.
US embassies in the region, including in Qatar, Bahrain and the UAE, have also advised their staff and US citizens to "shelter in place".
After the US warning, British embassies in those countries issued a similar warning to UK nationals "out of caution".
Saturday's attack follows mounting tension in the region, with the US deploying a vast fleet of warships and aircraft to try to pressure Iran into a deal over its nuclear programme.
Talks between the US and Iran regarding Tehran's nuclear programme ended on Thursday without agreement.
On Saturday, Israeli authorities said the strikes, dubbed Operation Roaring Lion by Israel and Operation Epic Fury by the US, were intended to "thoroughly degrade the Iranian terrorist regime and to remove existential threats to Israel".
In a video posted on his Truth Social platform, US President Donald Trump said the attacks were "a noble mission".
He said Iran had "attempted to rebuild their nuclear programme and to continue developing long-range missiles that can now threaten our very good friends and allies in Europe, our troops stationed overseas and could soon reach the American homeland".
The UK is reported to have previously resisted US requests to use the Diego Garcia base in the Indian Ocean to launch strikes on Iran.
Reform UK's Richard Tice demanded to know whether such a request had been refused again, saying a refusal would have "seriously damaged the special relationship" and praising the US and Israel for acting to "protect us all in the West by destroying the dangerous Iranian regime".
