SANAA, Yemen - The Saudi-led coalition fighting in Yemen closed off the land, sea and air ports to the country on Monday after a rebel-fired ballistic missile targeted Riyadh.

The coalition's statement ramps up tensions between the Sunni kingdom and its Shiite neighbor Iran, both of which have interests in Yemen's yearslong conflict. The bloodshed continued on Sunday as an Islamic State-claimed militant attack in Aden killed at least 21 people.

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

Iran has denied arming those rebels. The Houthi militants have said their Volcano-variant ballistic missile is locally produced.

Riyadh announced on Sunday to offer rewards worth around $400 million to those who provide information on 40 leaders of the Houthi militia in Yemen, Saudi Press Agency reported. The rewards will be given to those who provide information that leads to an arrest or who know the whereabouts of the wanted.

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 country to the brink of famine.

The Saudi-led coalition launched a wave of airstrikes - starting overnight and continuing until noon on 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.

There was no immediate response from Iran, though Iran's Defense Minister General 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 semiofficial ISNA news agency as saying on Sunday. The US has offered logistical and targeting support to the Saudi-led coalition.

Iran's Revolutionary Guard chief, Major General Mohammad Ali Jafari, said Iran can't transfer rockets to Yemen and stressed that the missiles were made there.

The Houthis said 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.

Aden attack kills 21

Meanwhile in Aden, masked militants claimed by an IS affiliate set off a large car bomb outside a security headquarters in Yemen's southern port city early on Sunday, killing at least 21 people before storming the compound, officials said. Fighting continued well into the night.

Aden is considered as Yemen's temporary capital and the Saudi-backed Yemeni government based itself there since 2015.

The al-Qaida and IS-linked terrorists took advantage of the security vacuum and ongoing civil war to expand their influence and seize more territories in Yemen.

AP - Xinhua