Britain’s foreign secretary has said that targeting cultural sites in Iran would breach international warfare conventions in an implicit rebuke to Donald Trump for threatening to bomb protected heritage sites.

Dominic Raab did not criticise the US president directly over his threats, but said: “We have been very clear that cultural sites are protected under international law and we would expect that to be respected.”

The senior British minister was speaking after Trump said he could target 52 Iranian sites if Iran retaliated over the assassination of Qassem Suleimani – “some at a very high level and important to Iran and the Iranian culture”.

To believe there’ll be world war three is to swallow US propaganda | Nesrine Malik Read more

Trump’s comments amount to threatening a war crime because such action would violate international treaties that the US has signed up to.

The president said that the number of targets chosen – 52 – matched the number of US hostages held by Iran in 1979, when a group of American diplomats and citizens were detained for 444 days in Tehran.

Historic sites in Iran include the ancient Achaemenid capital of Persepolis, founded in 518BC, a Unesco World Heritage site, and landmarks of the Islamic era such as the grand mosque of Isfahan.

Facebook Twitter Pinterest Persepolis, the ancient capital of the Achaemenid empire, in Shiraz, Iran. Photograph: Alireza Hosseinzadeh/Getty/iStockphoto

His threats prompted an angry response from Iran. President Hassan Rouhani said: “Those who refer to the number 52 should also remember the number 290. Never threaten the Iranian nation.” The number refers to the 1988 shooting down of a civilian plane – Iran Air Flight 655 – by a US warship stationed in the Gulf. The USS Vincennes had mistaken it for a hostile fighter jet; the incident led to the death of all 290 people on board.

The director general of Unesco, which lists 24 protected sites in Iran, highlighted that both the US and Iran were also signatories to a 1972 convention prohibiting states from taking “any deliberate measures which might damage directly or indirectly the cultural and natural heritage” of other states.

Audrey Azoulay met the Iranian ambassador to the organisation on Monday and “stressed the universality of cultural and natural heritage as vectors of peace and dialogue between peoples, which the international community has a duty to protect and preserve for future generations”.

The UN security council also passed a unanimous resolution in 2017 condemning the destruction of heritage sites following attacks by Isis, including on the ancient city of Palmyra in Syria and on the Mosul Museum in Iraq.

Nevertheless, Trump repeated the threat on Sunday, saying: “They’re allowed to kill our people, they’re allowed to torture and maim our people, they’re allowed to use roadside bombs and blow up our people, and we’re not allowed to touch their cultural sites? It doesn’t work that way.”

Raab was speaking immediately after a meeting of senior British ministers chaired by the prime minister, Boris Johnson, to discuss the Iran crisis. But his comments reflected an earlier briefing from Downing Street.

At lunchtime, Johnson’s spokesman said there were “international conventions in place that prevent the destruction of cultural heritage”, and implied that the UK did not believe such threats would be carried out.

Otherwise, Downing Street was careful not to criticise the president directly, insisting that Britain’s security partnership with the US remained “very close” despite Johnson not having been consulted prior to the assassination of Suleimani.

Asked if Johnson was convinced the US drone strike was legal, the spokesman said: “States have a right to take action such as this in self-defence, and the US have been clear that Suleimani was plotting imminent attacks on American diplomats and military personnel.”

The spokesman also defended Johnson’s failure to make any sort of statement on the assassination for 68 hours while he was holidaying with his partner on the Caribbean island of Mustique. “The PM was in contact with senior officials and senior ministers throughout the course of Friday, Saturday and Sunday,” he said.

Johnson also spoke to the Iraqi prime minister on Monday morning, urging him to allow foreign troops to remain in the country to fight against the threat posed by Islamic State.

“The coalition is in Iraq to protect Iraqis and others from the threat from Daesh [Isis] at the request of the Iraqi government,” the spokesman said. “We urge the Iraqi government to ensure the coalition is able to continue our vital work countering this shared threat.

“The foreign secretary spoke to the Iraqi president and prime minister this weekend. The prime minister is speaking with his Iraqi counterpart today and our ambassador in Baghdad is in touch with political leaders in Iraq to emphasise these points and urge them to ensure we can keep fighting this threat together.”