SANAA, Yemen (AP) — The Saudi-led coalition fighting in Yemen closed off the land, sea and air ports to the Arab world’s poorest country early Monday after a rebel-fired ballistic missile targeted Riyadh, blaming the launch on Iran and warning it could be “considered as an act of war.”

The coalition’s statement ramps up tensions between the ultraconservative Sunni kingdom and its Shiite rival Iran, both of which have interests in Yemen’s yearslong conflict. The bloodshed continued Sunday as an Islamic State-claimed militant attack in Aden killed at least 17 people.

In a statement, the coalition accused Iran of supplying Yemen’s Houthi rebels and their allies with the missile launched Saturday toward the Saudi capital’s international airport.

Iran has backed the rebels, but denies arming them. The Houthi militants have said their Volcano-variant ballistic missile is locally produced.

The Saudi-led coalition’s statement said the closures would be temporary and “take into account” the work of humanitarian and aid organizations. The war has claimed more than 10,000 lives and driven the Arab world’s poorest country to the brink of famine.

The Saudi-led coalition launched a wave of airstrikes — starting overnight and continuing until noon Sunday — on the rebel-held capital, Sanaa, apparently in response to the ballistic missile. Saudi Arabia said it shot down the missile, with fragments landing in an uninhabited area north of the capital.

The coalition threatened Iran with a possible retaliatory strike.

“Iran’s role and its direct command of its Houthi proxy in this matter constitutes a clear act of aggression that targets neighboring countries, and threatens peace and security in the region and globally,” the statement said. “Therefore, the coalition’s command considers this a blatant act of military aggression by the Iranian regime, and could rise to be considered as an act of war against the kingdom of Saudi Arabia.”

The statement added: “The coalition command also affirms that the kingdom reserves its right to respond to Iran in the appropriate time and manner.”

There was no immediate response from Iran, though Iran’s defense minister, Gen. Amir Hatami, earlier denied his country was involved in the launch.

“Does anyone ask the United States what are you giving to Saudi Arabia?” he was quoted by the semi-official ISNA news agency as saying Sunday. The U.S. has offered logistical and targeting support to the Saudi-led coalition.

President Donald Trump also was quick to blame Iran on Sunday. “A shot was just taken by Iran, in my opinion, at Saudi Arabia. And our system knocked it down,” Trump said, referring to the Patriot missile batteries Saudi Arabia purchased from the U.S.

Iran’s powerful Revolutionary Guard chief, Maj. Gen. Mohammad Ali Jafari, said Iran can’t transfer rockets to Yemen and stressed that the missiles were made there. He described Trump’s comments as “lies.”

The Houthis said in a statement that the missile was launched in response to bombings that have killed civilians. The Houthis have fired a number of missiles across the border in recent years, but this appeared to be the deepest strike yet within Saudi territory.

Meanwhile in Aden, masked militants claimed by an Islamic State affiliate set off a large car bomb outside a security headquarters in Yemen’s southern port city early Sunday, killing at least 17 people before storming the compound, officials said. Fighting continued well into the night.

Speaking on condition of anonymity because they were not authorized to brief reporters, the security officials said the militants placed snipers on the roof and gunned down most of the security forces inside. The officials gave conflicting accounts of what happened next inside the building. They initially said that the militants had taken an unknown number of people hostage. Later they said that they opened cell gates and released prisoners.

Security forces backed by an Apache helicopter continued to fight for control of the installation after nightfall, chasing down militants in the surrounding structures and neighborhood. Some hostages were killed, they added, without providing specific figures. They said at least five soldiers were among the dead.

Witnesses said at least four militant snipers could be seen on the roof of the compound. They also described mayhem as dead bodies littering the compound’s front courtyard couldn’t be retrieved because of the continuous sniper fire. Shallal al-Shayae, the security chief, was not inside the compound at the time of the attack, the officials said.

In an online statement, the local affiliate of the Islamic State group claimed responsibility for the attack saying they killed 50 soldiers and identified the bomber as Abu Othman al-Hadrami.

Yemen is embroiled in a war between Iran-backed Shiite rebels, known as Houthis, and the internationally recognized government, which is allied with a Saudi-led military coalition. The government has been based in Saudi Arabia since the Houthis overran the capital Sanaa in 2014. Government forces ostensibly control Aden, but the city remains volatile.