CAIRO -- Saudi Arabia's crown prince said Tuesday the ballistic missile launched by Yemen's Shiite rebels was a "direct military aggression by the Iranian regime" as the kingdom ordered the closure of all ports and grounded all humanitarian flights to Yemen, isolating the country further.
A Saudi-led military coalition, which has been at war with Yemen's Houthi rebels for more than two years, earlier tightened an air, land and sea blockade in response to the missile, which was intercepted near Riyadh but marked the rebels' deepest strike yet into Saudi territory.
The state-run Saudi Press Agency carried a statement on Crown Prince Mohammed bin Salman's call with British Foreign Minister Boris Johnson.
The kingdom has accused Tehran of supplying the missile fired toward Riyadh's international airport on Saturday night. Iran, which supports the Houthis but denies arming them, says it had nothing to do with the attack.
Human Rights Watch described the indiscriminate targeting of a predominantly civilian airport as an "apparent war crime."
"But this unlawful attack is no justification for Saudi Arabia to exacerbate Yemen's humanitarian catastrophe by further restricting aid and access to the country," said Sarah Leah Whitson, Mideast director for the New York-based watchdog.
Humanitarian flights to Yemen were grounded and ships ordered to leave, resulting in immediate price hikes on the streets of the rebel-held capital, Sanaa. The move threatens to worsen an already devastating humanitarian crisis in the country, where fighting has killed more than 10,000 civilians and displaced 3 million.
A U.N. official told The Associated Press the world body's flights were canceled, and that it was seeking "to resolve the issue as soon as possible." The official was not authorized to speak to the media so spoke on condition of anonymity.
The International Committee of the Red Cross urged for the reopening of ports for medical supplies. The relief agency said a shipment of chlorine tables used to prevent cholera, which has ravaged Yemen over the past months, didn't get a clearance at Yemen's northern border. More supplies are due next week, including 50,000 vials of insulin, ICRC said.
"Insulin cannot wait at a shuttered border since it must be kept refrigerated. Without a quick solution to the closure, the humanitarian consequences will be dire," said ICRC's regional director, Robert Mardini.
In announcing the closures earlier this week, Saudi Arabia had said it would take into consideration continuing aid efforts.
The Saudi-Houthi war dates back to 2014, when the Yemeni rebels and their allies swept down from their northern heartland and seized Sanaa, forcing the internationally recognized government to relocate to Saudi Arabia. The Saudi-led coalition controls Yemen's airspace but has made little progress on the ground, where the fighting has been stalemated for more than a year.
The tiny African nation of Djibouti has become the main transit point for humanitarian flights to Yemen. With the latest measures, however, flights are no longer being given clearance to leave, according to Doctors Without Borders.
The Houthis have nevertheless vowed to continue targeting Saudi Arabia as well as the United Arab Emirates, a key member of the coalition.
Col. Aziz Rashed, an army spokesman with a unit allied with the Houthis, warned travelers and travel agencies to stay away from Saudi and Emirati airports as they are considered "legitimate targets." Rashed claimed his military experts are able to develop missiles with ranges that exceed 1,500 kilometers (932 miles).
Drivers lined up in front of fuel stations across Sanaa Tuesday, fearing even worse fuel shortages. The price of fuel has already jumped from 5,500 riyals (about $20) to nearly 6,700 riyals (about $25) per liter. The Oil Ministry, controlled by the Houthis, issued a statement assuring residents they have enough fuel in storage.
On Monday night, the head of the World Food Program warned things will get worse with a prolonged, tightened blockade. David Beasley said his agency not only has trucks and planes grounded but also ships in the port of Hodeida. "The Saudi-led coalition is saying, 'get them out,'" he said.
Of Yemen's 17 million people who need food, the WFP is only reaching 7 million due to lack of funds and access by the Houthis and coalition alike, he said.
"If we are denied this access, even for two weeks, I can't imagine hundreds of thousands of children's lives are not going to be on the brink of starvation," Beasley said.
Associated Press writer Edith M. Lederer at the United Nations contributed to this report.