The UK was not informed in advance of the US airstrike that killed Iran’s top general, it has been claimed, as the British government scrambled to protect its interests in the Middle East in the wake of the attack.

The foreign secretary, Dominic Raab, said the government had “always recognised the aggressive threat posed by the Iranian Quds force”, whose leader Qassem Suleimani was killed in the strike.

Urging all parties to de-escalate the situation, he added: “Further conflict is in none of our interests.”

Raab discussed the dramatic ratcheting up of tensions with Donald Trump’s secretary of state, Mike Pompeo, in the aftermath of the attack.

But Tom Tugendhat, the chair of the foreign affairs committee in the last parliament, complained that the US was routinely failing to keep the UK informed of such decisions in advance.

Tugendhat told BBC News: “I’ve long believed that the purpose of having allies is that we can surprise our enemies and not each other, and it’s been a pattern, sadly, which has been a bit of a shame, that the US administration of late has not shared with us, and that is a matter of concern.”

Urging the US administration to “share much more closely with allies” in the future, he added: “The government needs to make some very quick choices on the safety of citizens overseas and the security of British personnel.”

It has been reported that Boris Johnson, who has been celebrating the new year on the private Caribbean island of Mustique, was unaware that the attack was due. The prime minister made no immediate comment.

Ministry of Defence and Foreign Office officials have begun reviewing measures to protect 400 soldiers based in Iraq, as well as British citizens and diplomats there. UK bases in the Middle East have been put on a state of heightened alert.

The Foreign Office advised British-Iranian dual nationals against any travel to Iran, and other British nationals to seek further advice before travelling there.

Jeremy Corbyn called the killing an assassination and said it represented “an extremely serious and dangerous escalation of conflict in the Middle East with global significance”.

The Labour leader said: “The UK government should urge restraint on the part of both Iran and the US and stand up to the belligerent actions and rhetoric coming from the United States. All countries in the region and beyond should seek to ratchet down the tensions to avoid deepening conflict, which can only bring further misery to the region, 17 years on from the disastrous invasion of Iraq.”

He later said he had written a letter to Johnson demanding an urgent privy council briefing and answers to seven urgent questions, including: the contact the UK government had with the US administration before and after the attack; whether the UK government had been in touch with the UN to discuss the consequences for peace and security; the measures taken to ensure the safety of UK nationals; and what assessment had been made of the potential increase in the risk of terrorist attack in the UK.

Corbyn has previously been criticised for his views on Iran. In the past he has been paid for appearances on the Iranian state broadcast network Press TV. He has said he used the opportunity to raise the issue of human rights in Iran and around the world.

Labour leadership hopefuls called for calm and for the government to press through the UN for no further escalations.

Emily Thornberry said the Foreign Office’s call for restraint was “too little and far too late in the wake of such a brazen, unlawful and provocative attack”. Clive Lewis called on Johnson “to condemn this cowboy action”, and Rebecca Long – Bailey echoed Corbyn’s “assassination” comment and warned that Trump was “pushing us closer to the brink of another disastrous war”.

Keir Starmer, who has not yet declared he will run for Labour leader, said it was an “extremely serious situation” and urged the government to “engage, not isolate” Iran. Another possible leader, Lisa Nandy, said: “World leaders must stand up to Trump.”