Foreign Secretary Dominic Raab has urged Iran to “take a diplomatic route” to reduce tensions following the US killing of Iran’s top military leader.
Mr Raab said the UK understood why the US killed Qasem Soleimani in a drone strike in Iraq last week, and the US “had a right to exercise self-defence”.
Iraqi MPs have since called for foreign troops to leave the country.
And the US-led coalition against the Islamic State group said it will not be training local allies.
Instead, it said it would focus for now on protecting Iraqi bases that host US, UK and other coalition troops.
Prime Minister Boris Johnson is due to return to the UK later and will talk to foreign leaders in the coming days.
Soleimani, who had been head of the elite Iranian Quds Force, died in the drone strike in Baghdad on Friday.
Tehran has vowed to avenge the general’s killing. The US has pledged to send 3,000 extra troops to the region while the UK has 400 troops in the Middle East.
Speaking to the BBC’s Andrew Marr programme on Sunday, Mr Raab rejected the idea the killing was an act of war, adding: “Iran has for a long period been engaged in menacing, de-stabilising activities.”
Pressed on whether the killing was legal, Mr Raab said: “My view is – and the operational assessment has been done by the Americans – is that there is a right of self-defence.
“It was General Soleimani’s job description to engage proxies, militias across not just Iraq but the whole region, not just to destabilize those countries but to attack Western countries… In those circumstances the right of self-defence clearly applies.”
Mr Raab said he first became aware of the killing of Soleimani “as it happened” and spoke to US counterpart Mike Pompeo – who he will meet for pre-arranged talks in Washington this week – on Friday.
Mr Raab is also expected to meet his French and German counterparts before travelling to the US.
Mr Raab said the “important thing now is to de-escalate the tensions and try and restore some stability” – while trying to contain Iran’s “nefarious actions”.
“We also need to see that there’s a route, a door left ajar for a diplomatic solution so that when the leadership in Tehran wake up to their options, they understand there is a positive route through for them.”
Asked about the criticism over Mr Johnson being on holiday, Mr Raab said he had been “in constant contact with the prime minister over the Christmas break on a whole range of foreign policy issues”.
Mr Johnson has yet to speak publicly about the US airstrike or threats from Iran.