Saudi Arabia's Crown Prince Mohammed bin Salman has accused Iran of an act of "direct military aggression" by supplying missiles to rebels in Yemen.
This "may be considered an act of war", state media quoted the prince as telling UK Foreign Secretary Boris Johnson in a telephone conversation.
On Saturday, a ballistic missile was intercepted near the Saudi capital, says a BBC report on Tuesday.
Iran has denied arming the Houthi movement, which is fighting a Saudi-led coalition backing Yemen's government.
Foreign Minister Mohammad Javad Zarif said on Monday that Saudi Arabia's "wars of aggression" and "regional bullying" were threatening the Middle East.
Houthi-aligned media reported that the rebels had fired a Burkan H2 ballistic missile at King Khaled International Airport, which is about 850km (530 miles) from the Yemeni border and 11km north-east of Riyadh, on Saturday evening.
Saudi media reported that missile defences intercepted the missile in flight, but that some missile fragments fell inside the airport area. No casualties were reported.
Human Rights Watch said the launch of an indiscriminate missile at a predominantly civilian airport was an apparent war crime.
The official Saudi Press Agency reported on Tuesday that in his telephone call with Prince Mohammed, Johnson had "expressed his condemnation of launching a ballistic missile by Houthi coup militias" and affirmed "Britain's stand with the kingdom of Saudi Arabia in confronting security threats".
"For his part, the crown prince stressed that the involvement of the Iranian regime in supplying its Houthi militias with missiles is considered a direct military aggression by the Iranian regime and may be considered an act of war against the kingdom," it added.
Saudi Foreign Minister Adel al-Jubeir told CNN on Monday that Lebanon's Hezbollah movement, an Iranian proxy, was also involved.
"It was an Iranian missile launched by Hezbollah from territory occupied by the Houthis in Yemen," he said.