CAIRO (AP) — Saudi Arabia's crown prince said Tuesday the ballistic missile launched at the kingdom by Yemeni rebels was a "direct military aggression by the Iranian regime," as the Saudi-led coalition ordered the closure of all ports and grounded all humanitarian flights to the war-torn country.

The military coalition, which has been at war with Yemen's Houthi rebels for more than two years, has 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.

Crown Prince Mohammed bin Salman's remarks were carried by the Saudi Press Agency.

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.

The U.S. ambassador to the United Nations, Nikki Haley, urged the Security Council to hold Iran accountable for a missile she said it had supplied to the Houthis in July. Haley said the missile used Saturday may also have been Iranian.

"The United States is committed to containing Iran's destabilizing actions and will not turn a blind eye to these serious violations of international law by the Iranian regime," she said. The U.S. supports the Saudi-led coalition.

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.

U.N. spokesman Stephane Dujarric called on the coalition and the rebels to allow aid in, warning that "any further shocks to imports of food and fuel may reverse recent success in mitigating the threat of famine."

"All parties to the conflict must allow and facilitate safe, rapid, unhindered humanitarian access to all people in need, through all ports and airports," Dujarric told reporters at U.N. headquarters in New York.

Yemeni officials meanwhile said suspected Saudi-led air raids killed at least 23 people in the rebel-controlled northern province of Hajjah. They said the strikes targeted homes of local sheikhs where the head of the Houthis' Supreme Political Council, Saleh al-Sammad, was visiting.

The dead included women and children, and at least three people were wounded, they added, speaking on condition of anonymity because they were not authorized to brief reporters. Houthi spokesman Mohamed Abdel Salam denied Saudi media reports that al-Sammad was killed.

Humanitarian flights to Yemen were grounded and ships ordered to leave, resulting in immediate price hikes in 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 that aid flights were canceled, and said the U.N. 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 the reopening of ports for medical supplies. The relief agency said a shipment of chlorine tables used to prevent cholera, which has ravaged Yemen in recent months, did not get a clearance at Yemen's northern border. More supplies are due next week, including 50,000 vials of insulin, the 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 the ICRC's regional director, Robert Mardini.

In announcing the closures earlier this week, Saudi Arabia said it would take into consideration continuing aid efforts.

The 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 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 around $20 to $25 per liter. The Oil Ministry, controlled by the Houthis, issued a statement assuring residents it has 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.

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Associated Press writer Edith M. Lederer at the United Nations contributed to this report.