Saudi crown prince accuses Iran of 'direct aggression'
"The involvement of Iran in supplying missiles to the Houthis is a direct military aggression by the Iranian regime," the Saudi Press Agency quoted the crown prince as saying during a telephone conversation with British Foreign Secretary Boris Johnson.
This "could be considered as an act of war," Prince Mohammed said.
Saudi forces on Saturday intercepted and destroyed a ballistic missile near Riyadh international airport, reportedly fired from Yemen by the Houthi rebels.
It was the first reported Houthi missile launch to reach Riyadh and threaten air traffic, underscoring the growing threat posed by the conflict on Saudi Arabia's southern border.
Riyadh accused Tehran of supplying ballistic missiles to the Houthi rebels. Iran denied the allegation.
The regional rivals traded accusations on Monday with Saudi Arabia saying the missile attack might amount to an act of war and Tehran accusing Riyadh of war crimes in Yemen.
Saudi Arabia has led a military intervention in Yemen since 2015 in support of its internationally recognised government.
More than 10,000 people have since been killed since the military intervention, according to the United Nations.
A cholera outbreak has claimed more than 2,100 lives in Yemen since April as hospitals struggle to secure supplies amid a coalition air and sea blockade.
The UN has warned Yemen now stands on the brink of famine.
The coalition was briefly included on the annual list of shame last year before a threat by Saudi Arabia to cut off its funding to UN programmes forced a reversal.
Human rights groups have urged governments backing the coalition, including the US, UK and France, to suspend all weapons sales to the Gulf monarchy.
Tensions have been rising between Sunni-ruled Saudi Arabia and predominantly Shia Iran, which back opposing sides in wars and power struggles from Yemen to Syria.