Jeremy Hunt has insisted he is doing what he can amid heightened tensions between the US and Iran.
The Foreign Secretary was warned he cannot be “completely absent from the stage” by David Miliband, who described the situation as a “pressing global threat to peace and security”.
Mr Hunt, who is battling to become the next prime minister, said he is speaking to counterparts “regularly” about the Iran crisis which he called “extremely serious”.
Foreign Office minister Andrew Murrison is holding talks with the Tehran government on Sunday and is expected to call for “urgent de-escalation”.
The trip was announced after Donald Trump said the US was “cocked and loaded” to retaliate against Iran for downing an American drone.
The strikes were reportedly called off 10 minutes before they were to be carried out on Thursday after Mr Trump was told 150 people could die.
On Saturday, a spokesman for Iran’s armed forces warned that a military strike would “set the region ablaze and burn up the US, its interests, and its allies”.
Mr Trump later tweeted that the US will impose “major additional sanctions” on Iran on Monday after opting to halt military action “from going forward at this time”.
Former Labour foreign secretary Mr Miliband told BBC One’s The Andrew Marr Show: “The current Foreign Secretary has real responsibilities at the moment.
“I don’t think we can afford him to be completely absent from the stage. Britain is a permanent member of the security council. This is a pressing global threat to peace and security.
“We’re relying on the caution of President Trump to keep the hawks at bay in his own administration.”
Responding to what Mr Miliband said, Mr Hunt wrote on Twitter: “Agree, and thankfully I’m not. Speaking regularly to my counterparts on this subject, including Sec Pompeo, have sent a minister to the region, and will be updating parliament on Tuesday. Extremely serious situation.”
Dr Murrison’s visit amid the bellicose exchanges between Washington and Tehran is part of the UK’s “ongoing diplomatic dialogue with Iran”, the Foreign and Commonwealth Office (FCO) said on Saturday.
“At this time of increased regional tensions and at a crucial period for the future of the nuclear deal, this visit is an opportunity for further open, frank and constructive engagement with the government of Iran.
“Dr Murrison will call for urgent de-escalation in the region and raise UK and international concerns about Iran’s regional conduct and its threat to cease complying with the nuclear deal to which the UK remains fully committed.”
Mr Trump pulled out of a long-term deal struck with Iran in 2015 to limit its sensitive nuclear activities and allow in international inspectors in return for the lifting of economic sanctions.
The deal was signed by his predecessor Barack Obama along with the UK, France, China, Russia and Germany, which still support the agreement.
But Mr Trump declared it a “terrible” deal and imposed more sanctions.
On Saturday, German chancellor Angela Merkel called for a “political solution” on Iran, saying such a result “should not just be a hope, but it should be worked towards with the utmost seriousness”.
Tensions between the US and Iran have increased in recent weeks amid claims by Washington that Tehran has been behind attacks on oil tankers in the Persian Gulf.
Iran cannot have Nuclear Weapons! Under the terrible Obama plan, they would have been on their way to Nuclear in a short number of years, and existing verification is not acceptable. We are putting major additional Sanctions on Iran on Monday. I look forward to the day that…..
— Donald J. Trump (@realDonaldTrump) June 22, 2019
Dr Murrison’s visit also takes place amid continuing tension between London and Tehran over the treatment of Nazanin Zaghari-Ratcliffe, a British-Iranian dual citizen who has been detained in Iran since April 2016 accused of spreading propaganda against Iran.
Her husband Richard Ratcliffe has been on a hunger strike outside the Iranian Embassy in London in support of his wife who is also on hunger strike.
Speaking about Dr Murrison’s planned visit to Iran, Mr Ratcliffe told the Press Association: “I’ve been asked how hopeful I am. I’m not sure if I’m hopeful, but certainly will be watching very closely to see how things develop and what comes back.”