Yemen’s armed Houthi movement has said  it could attack warships and oil tankers from enemy countries in retaliation against the closure of Yemeni ports by a Saudi-led military coalition last week.

Saudi Arabia has blamed the Iran-allied Houthis for firing a ballistic missile towards Riyadh airport on Nov 4. Two days later, the Saudi-led coalition responded by closing access to Yemeni ports, saying this was needed to stop arms reaching the Houthis.

The United Nations says the closure could cause a famine in Yemen that could kill millions of people if ports are not reopened.

“The battleships and oil tankers of the aggression and their movements will not be safe from the fire of Yemeni naval forces if they are directed by the senior leadership (to attack),” the Houthis’ official media outlet Al Masirah said on its website, citing a military commander.

Yemen lies beside the southern mouth of the Red Sea, one of the most important trade routes in the world for oil tankers, which pass near Yemen’s shores while heading from the Middle East through the Suez Canal to Europe.

The Houthis, fighters drawn mainly from Yemen’s Zaidi Shi‘ite minority and allied to long-serving former president Ali Abdullah Saleh, control much of Yemen including the capital San‘aa. The Saudi-led military alliance is fighting in support of the internationally recognised government of President Abd-Rabbu Mansour Hadi, who is based in the southern port of Aden.

Al Masirah said the decision to threaten coalition vessels was taken after a meeting of naval officials who had discussed the possible response to the closure of Yemeni ports.

Houthi leader Abdel-Malek al-Houthi said in September his group could target Saudi oil tankers should the coalition attack Yemen’s main port at Hodeidah.

On Sunday, the head of the Houthi supreme revolutionary committee, Mohammed Ali al-Houthi, wrote on his Facebook page that the Houthis would target oil installations in Saudi Arabia with missiles if the coalition attacked Hodeidah.

The Houthis have often made such threats against Saudi Arabia and its main coalition partner, the United Arab Emirates, although they have not so far demonstrated the capability to hit all the targets they mention.

The missile which was intercepted on Nov. 4 has escalated tensions between regional foes Saudi Arabia and Iran, which Riyadh blames for supplying the missile to the Houthis.

Iran denies it supplies arms to the Houthis but has said the missile was a reaction to Saudi “aggression”.

The Saudi-led coalition has said aid workers and supplies would continue to be able to access Yemen despite the closure of its ports, but aid agencies say they have not been able to get through and have warned of famine and a health catastrophe.

The coalition opened a land border crossing on Thursday between Saudi Arabia and territory held by the Saudi-backed government, and the port at Aden was reopened on Wednesday. But ports in Houthi-held areas have remained shut.