PARIS — Yemen’s Iran-backed Houthis have built up a missile and drone arsenal capable of launching varied and sustained strikes, as Saudi Arabia and the Yemeni government it backs are finding out.

Since early September, the Houthis have struck key oil infrastructure and airports across Saudi Arabia, notably Riyadh’s airport, which has been targeted 20 times.

They have also unsuccessfully targeted the cities of Medina and Mecca.

The trigger for their return to hostilities, after a four-year truce, was a Saudi bombardment of the airport in Sanaa, Yemen’s capital, in July to prevent a Houthi delegation from landing there.

Since then, there have been “tit-for-tat” military strikes, said April Longley Alley, a specialist on Yemen at the Washington Institute think tank.

“The Houthis framed this campaign as blockade for blockade, airport for airport, escalation for escalation,” she said.

The Houthis possess a wide range of ballistic missiles and drones, which they are also using to strike targets in the Bab al-Mandab Strait at the entrance to the Red Sea.

The group’s missile stocks partly come from arsenals seized when it took Yemen’s capital, Sanaa, in 2014, as well as “whole systems smuggled in, or self-manufactured systems built from parts that were themselves smuggled into Yemen, primarily via the Arabian Sea”, explained Niranjan BS, a strategic weapons analyst at Jane’s, the open-source intelligence company.

According to the International Institute for Strategic Studies’ Military Balance database, the Houthis have several types of medium-range missiles, some derived from Iranian models such as the Kheibar Shekan.

They also have short-range missiles, including the Asef anti-ship missile, derived from Iran’s Khalij Fars class of missile, noted the Wilson Center think tank.

In addition, the Houthis have a range of cruise missiles from Iran’s Quds missile family, with the Version 4 believed to have a range of 2,000 kilometres (1,200 miles), according to the Wilson Center.