BORIS Johnson has issued a thinly-veiled warning to Donald Trump not to attack Iran’s cultural sites, which under international law could be regarded as a war crime.

The US President has told Tehran that if it ordered any retaliation on US interests following the death of Iran’s top general Qasem Soleimani, then dozens of its cultural sites could be targeted.

Mr Trump stressed any military response from Iran would face “major retaliation”.

He has tweeted how the US has drawn up a target list of 52 Iranian sites, some "at a very high level and important to Iran and the Iranian culture" if Tehran undertook any strike on American assets.

He told reporters: “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."

No 10 is keen to stress how Mr Johnson’s primary focus now is, along with that of his fellow EU leaders, to urge restraint and de-escalation of tensions in the Middle East.

His spokesman said: “The PM has been very clear on two points: Soleimani posed a threat to all of our interests and is responsible for a pattern of disruptive, destabilising behaviour in the region but there is now an urgent need for de-escalation and that is why we have called on all sides to exercise restraint and prevent further conflict.”

Asked if the Prime Minister had urged restraint on the US President during their phonecall yesterday, the spokesman said he had not listened in to that particular call but noted that Mr Johnson’s statement and the joint one with France and Germany showed the UK was “urging restraint on all sides”.

But questioned about Mr Trump’s renewed threat on Iran’s cultural sites, he stressed: “There are international conventions in place that prevent the destruction of cultural heritage.”

The 1954 Hague Convention for the protection of cultural property in the event of armed conflict was drawn up under the auspices of the United Nations.

Its guiding principle is that “any damage to cultural property, irrespective of the people it belongs to, is a damage to the cultural heritage of all humanity, because every people contributes to the world's culture”.

While the US is a signatory to the initial Hague Convention, it is not one to the First and Second Protocols, which cover the enhanced protection of cultural sites during conflict; the UK and Iran are.

In 2016, a terrorist, who helped damage and destroy nine mausoleums and one mosque in Timbuktu in Mali, was charged with and pleaded guilty to the war crime of intentionally directing attacks against historic monuments and buildings dedicated to religion and was sentenced to nine years' imprisonment.

Meanwhile, No 10 said the PM this morning had had a phonecall with Adel Abdul-Mahdi, his Iraqi counterpart, and agreed to "work together to find a diplomatic way forward" to the Iran crisis.

“The leaders discussed the need to de-escalate tensions in the region following the death of Qasem Soleimani and agreed to work together to find a diplomatic way forward.

“The Prime Minister underlined the UK’s unwavering commitment to Iraq’s stability and sovereignty and emphasised the importance of the continued fight against the shared threat from Daesh,” it added.

Mr Johnson is due this afternoon to discuss the Iran crisis with Dominic Raab, the Foreign Secretary, and Ben Wallace, the Defence Secretary, along with senior officials, including Sir Mark Sedwill, the Cabinet Secretary.

It is expected that tomorrow Mr Raab will update MPs with a Commons statement. He is due to hold talks with his American counterpart, Mike Pompeo, during a visit to Washington on Thursday.

A National Security Council meeting is set to take place tomorrow after the usual 930am Cabinet.

During a regular Downing St briefing for journalists, the PM’s spokesman was asked if Mr Johnson was 100 per cent certain the US attack was legal. He replied: “As the Foreign Secretary set out yesterday, states have a right to take action such as this in self-defence and the US have been clear Soleimani was plotting imminent attacks on American diplomats and military personnel.”

Asked about the fact the UK Government was not pre-warned about Thursday’s drone attack at Baghdad Airport, the spokesman said: “Look, we have a very close security partnership with the US. We’re in regular dialogue at every level.”

Asked if David Cameron had not contacted the US before the UK drone strike in Syria in 2015, which killed two Britons fighting alongside Daesh terrorists, he replied: “That’s not the sort of thing I would comment on.”

No 10 stressed how UK forces were in Iraq at the invitation of the Baghdad Government to counter the threat of Daesh. “We urge the Iraqi Government to ensure the coalition is able to continue our vital work to counter this threat,” added the spokesman.

Elsewhere, Lord Campbell, the former Liberal Democrat leader, ahead of a Lords debate on the Iran crisis in the upper chamber tomorrow, expressed deep concern about the potential for military conflict in the Middle East.

The Scottish peer told The Herald: “Trump has firmly put the ball in the Iranian court. Tehran now has an almost unfettered decision on how it responds.

“Given the international disturbances of recent weeks, there is no doubt that a substantial and potentially very dangerous reaction could be expected.

“But don’t rule out the possibility of the drastic impact there would be if the Strait of Hormuz became impassable for oil tankers given a large amount of the world’s oil passes through it. The impact would be just as damaging to Trump as a serious terrorist attack,” he added.