CAIRO -- The United States on Wednesday joined Saudi Arabia in accusing Iran of supplying Yemen's Houthi rebels with advanced weapons including a ballistic missile that struck the Saudi capital last week.

The White House statement says the U.S. condemns the Iranian government's activities and stands with Saudi Arabia and other Persian Gulf partners against Iran's aggression and "blatant" violations of international law.

It says missile systems were not present in Yemen before the civil war there, alleging that Iran provided them. The statement also urges the United Nations to review evidence that Iran is perpetuating the war in Yemen to further its regional ambitions.

The remarks came one day after Saudi Arabia's crown prince said that a ballistic missile fired at the kingdom by Yemeni rebels was a "direct military aggression by the Iranian regime."

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In response to the Houthis' missile assault, a Saudi-led coalition announced it has closed all ports in Yemen as of Monday, sparking U.N. concerns as all humanitarian flights have also been grounded, with trucks stuck at crossings and ships carrying basic necessities like fuel, wheat and other food have been ordered to leave.

The U.N. warned that the shut-down of the ports could exacerbate the already difficult humanitarian crisis, as the war has already brought the country to the brink of famine.

A Saudi-led military coalition has been at war with the Iranian-backed Houthis for more than two years. The Houthis control northern Yemen while the internationally recognized government of Abed Rabbo Mansour Hadi's grip over the southern region has been weakened. Hadi is backed by the Saudi-led coalition.

Officials including a top military commander close to Hadi told The Associated Press that oil-rich Saudi Arabia has prevented Hadi, his sons, officials and ministers from returning to Yemen. The ban was prompted by the bitter enmity between Hadi and the United Arab Emirates, they said, speaking on condition of anonymity because of the sensitivity of the subject.

The Yemeni presidency on Wednesday issued a statement denying that, saying the reports are "lies."

Quoting an unnamed official, the statement said the reports are a "systematic campaign targeting Saudi Arabia which leads a battle to stop the Iranian interference in Yemen and the region." The Saudis and the UAE are the main pillars of the coalition.