LONDON — Saudi Arabia charged Monday (Nov 6) that Iran had committed “a blatant act of military aggression” by providing its Yemeni allies with a missile fired at the Saudi capital over the weekend, raising the threat of a direct military clash between the two regional heavyweights.

The accusations represent a new peak in tensions between Saudi Arabia and Iran at a time when they are already fighting proxy wars in Yemen and Syria, as well as battles for political power in Iraq and Lebanon.

The Saudi statement said the missile could be considered an “act of war” against the kingdom and triggered its right to self-defence under international law.

It claimed that the rocket, which was fired from Yemen and intercepted en route to Riyadh, the capital, had originated in Iran.

The Saudis said that “experts in military technology” had examined the debris of the missile, as well as one launched in July, and “confirmed the role of Iran’s regime in manufacturing these missiles and smuggling them to the Houthi militias in Yemen for the purpose of attacking the kingdom.”

United States officials have previously accused Iran of arming its Yemeni allies, the Houthis. But Saudi Arabia’s claims could not be independently verified.

Saudi Arabia and its allies, including the US and the United Arab Emirates, have enforced a sea and air blockade around Yemen since the outbreak of the current war there, so it was also unclear how Iran could have provided large weapons like ballistic missiles.

The top commander of the Islamic Revolutionary Guards Corps in Iran called the accusation “baseless.”

“These missiles were produced by the Yemenis and their military industry,” Major General Mohammad Ali Jafari told the semi-official news agency Tasnim.

Iran’s foreign minister Mohammad Javad Zarif accused Saudi Arabia of “wars of aggression, regional bullying, destabilising behaviour & risky provocations,” in a statement on Twitter.

Saudi Arabia “bombs Yemen to smithereens, killing 1000s of innocents including babies, spreads cholera and famine, but of course blames Iran,” Mr Zarif said.

The Saudi claim was the second time in three days that the kingdom and its allies have accused Iran of trying to destabilise the region.

On Saturday, hours before the missile was intercepted, Lebanese Prime Minister Saad Hariri resigned his post in protest of Iranian interference in Lebanon through its client, Hezbollah.

Mr Hariri tendered his resignation via a televised statement from Saudi Arabia and has not yet returned to Beirut, leading to the widespread assumption in Lebanon that he was pressured to resign by the Saudis, his political patrons.

Mr Hassan Nasrallah, the leader of Hezbollah, said over the weekend that the Saudis had all but kidnapped Mr Hariri. Mr Nasrallah urged Mr Hariri to return to Beirut for power-sharing talks “if he is allowed to come back.”

“It was definitely a Saudi decision that was imposed on him,” Mr Nasrallah said. “It was not his will to step down.”

The accusations of Iranian interference in Yemen and Lebanon came as the Saudi crown prince was further consolidating his power with a wave of internal arrests that began around midnight Saturday (Nov 4) and expanded Monday, trapping 11 princes and dozens of others in a Ritz Carlton hotel now serving as a uniquely luxurious prison.

The arrests cemented the dominance of the crown prince, Mohammed Salman, 32, over military, foreign, internal security, economic and social affairs inside the kingdom.

In the 2 1/2 years since the coronation of his father, King Salman, 81, Crown Prince Mohammed has sharply escalated a cold war with Iran, stepping up Saudi Arabia’s efforts to push back Iranian influence in the Syrian civil war, plunging the kingdom into a protracted military conflict against Iranian-allied forces in Yemen, and isolating neighbouring Qatar in part for being too close to Iran.

His hawkish stance toward Iran and to Islamists in the region also appears to have formed the basis for a close bond with US President Donald Trump, who visited Riyadh this year and maintained a conspicuous silence over the weekend about the crown prince’s campaign of extrajudicial arrests.

The connection between the arrests in Saudi Arabia and the accusations against Iran was unclear, raising questions Monday about whether the crown prince was emboldened to take on Iran by his success at checking his internal rivals, or whether he had hastened to check potential domestic critics in order to fortify his hand for a regional confrontation.

Mr Joseph Kechichian, a scholar at the King Faisal Centre for Research and Islamic Studies in Riyadh who is close to the royal family, said the moves represented the convergence of two long-term agendas for Crown Prince Mohammed.

“Inside he has been able to put his men into positions of influence and he has pushed aside his rivals,” Mr Kechichian said. “And ever since President Trump’s visit to Riyadh there has been a very consistent policy with the essential coordination of the United States, and Iran is in the bull’s-eye.”

“In the past, accommodation was the name of the game, and today confrontation is the name of the game,” he said.

Saudi Arabia also said on Monday that it would “temporarily” close Yemen’s land, sea and air ports of entry in response to the missile firing, in order to tighten inspections and stop any weapons shipments. It pledged to provide for “the continuation of the entry and exit of humanitarian supplies and crews.”

However, the United Nations (UN) said that two aid flights scheduled for Monday had not been allowed to depart for Yemen.

“We’re trying to see whether we can get our normal access restored,” Mr Farhan Haq, a UN spokesman, said at a daily briefing. “We underscored to all parties the need for regular humanitarian access.”

The United Nations considers Yemen, the Middle East’s poorest country, one of the world’s biggest humanitarian emergencies. Roughly 17 million people — 60 per cent of the population — need food assistance, and 7 million are at risk of famine. Nearly 900,000 Yemenis have been sickened by cholera.

Saudi Arabia accompanied its accusations against Iran with the announcement that it would pay bounties of up to US$30 million (S$40.86 million) for information leading to the capture of 40 Houthi leaders in Yemen.

“We fear nothing,” one leader on the list, Mr Mohammad Ali Houthi, said in a defiant speech Monday in the Yemeni capital, Sanaa.

He called the sweep of arrests ordered by Crown Prince Mohammed “a coup leading to the throne” and invited any dissident Saudis to take refuge in Yemen. “We tell the citizens and princes in Saudi Arabia that the Yemeni people are opening their arms to you. None will endure injustice.”

Yemen’s Houthi-controlled Defence Ministry said over the weekend that its forces had targeted Riyadh’s airport with a long-range missile. Immediately after the firing, the Saudi-led coalition hit Sanaa with the heaviest barrage of airstrikes in more than a year. THE NEW YORK TIMES