The US and Saudi governments have made a joint public appeal to the UN Security Council to extend the 13-year old arms embargo on Iran or risk a renewed arms race in the Middle East.
"Iran has not earned the trust to have the embargo lifted... The last thing this region needs is more Iranian weapons," said Brian Hook, President Donald Trump's special representative on Iran during a joint press conference in Saudi Arabia. Mr Hook stood alongside Adel Jubeir, Saudi Arabia's minister of state for foreign affairs.
Parts of what were said to be missiles fired by Houthi rebels in Yemen were laid out behind them. Nearly 400 missiles and rockets have been fired from Yemen into Saudi Arabia, said Mr Hook, adding that this would not have been possible without assistance from Iran.
The joint press conference made no mention of the £5.3bn ($6.5bn) worth of arms reportedly sold by the UK to Saudi Arabia since the Yemen war accelerated in March 2015, nor of the large number of Yemeni civilians killed by Saudi-led coalition airstrikes, drawing widespread international criticism.
The US has been, for many years now, the largest supplier of weapons to the Gulf region but Iran has managed to defy stringent sanctions by exporting both military hardware and advisers to its proxies in the region, notably Hezbollah in Lebanon and the Houthis in Yemen.
"We call on the UN Security Council to extend the arms embargo on Iran," said the US envoy, warning that if the embargo were allowed to lapse then Iran would be able to export "battle tanks, artillery, combat aircraft, attack helicopters, drones and missile systems to its proxies", as well as upgrading the range and lethality of its weapons systems and posing what he said would be an even greater threat to shipping in the region.
"No leader I have spoken to thinks this is a good idea."
A recent study by the International Institute for Strategic Studies (IISS) concluded that despite being under sanctions Iran had succeeded in gaining the strategic advantage over its rival, Saudi Arabia.
The disparity in wealth between the two countries is enormous, with the richer Saudis expending billions of dollars on expensive and sophisticated state-of-the-art weaponry. Yet none of this was able to prevent a devastatingly effective missile and drone attack on Saudi Arabia's critical oil infrastructure last September. In the space of just a few minutes a flurry of missiles fired under cover of darkness temporarily took out half of Saudi oil exports.
"These missiles were Iranian," declared Adel Jubeir today. "They came from the north."
The attack was a wake-up call to the Saudi government that US-supplied air defences could not necessarily protect the country from a concerted "swarm" attack by low-tech weapons. It also helped prompt a Saudi realisation that its military campaign in Yemen was probably unwinnable and that a political solution to that war was the only way to end it.
While the Saudis and their Western allies have supported the UN-recognised Yemen government-in-exile, Iran has supplied weaponry and advice to the Houthi rebels who still control most of the more populated areas. Aid agencies have warned of a looming catastrophe if the conflict continues.
On Tuesday, said Mr Hook, UN experts will present their findings to the UN Security Council. He said Iran had committed numerous violations of multiple UN arms embargos. "If this is what Iran is doing now," said the US envoy, "imagine what they will do if restrictions are lifted?"
The BBC has asked the Iranian government for comment.