Who are the Houthis, and why are they so hard to fight?

Saudi Arabia's energy minister has vowed to respond to the attacks on the kingdom's airports and oil and gas facilities by Yemen's Iran-backed Houthi movement. It comes after the Houthis fired missiles in strikes across Riyadh, killing at least 14 and injured more than 300 in two strikes on the city's airport. They also attacked oil facilities and Dammam airport in eastern Saudi Arabia, their military spokesman Brig Gen Yahya Saree said. The Houthis said they launched the attacks in retaliation for "brutal Saudi aggression" against areas they control in western Yemen. The BBC's security correspondent Frank Gardner explains how Houthis' precision strikes and guerrilla tactics have made it difficult for Saudi forces to gain the upper hand.

Saudi Arabia's energy minister has vowed a "serious" response to the deadly attacks on the kingdom's airports and oil and gas facilities by Yemen's Iran-backed Houthi movement. "The events of recent weeks are serious. Our response must be equally serious," Prince Abdul Aziz bin Salman told the WPC Energy Congress in Riyadh. On Sunday, a Pakistani man was killed in an attack on a terminal at the capital's King Khalid International Airport, Saudi authorities said. It came a day after a Houthi missile hit another terminal, killing 13 people and forcing its closure. The Houthis said they launched the attacks in retaliation for "brutal Saudi aggression" against areas they control in western Yemen. The Houthi-run health ministry said a child was killed and six other people were injured in a Saudi air strike on a home in the capital, Sanaa, on Sunday. A Saudi-led coalition has been providing air support for Yemeni pro-government forces battling the Houthis on Yemen's Red Sea coast and other areas.

Two strikes on the international airport in the Saudi capital of Riyadh have left 14 dead and more than 300 injured. There have been a series of other attacks earlier in the week. CCTV footage from inside King Khalid International Airport shows people taking cover as one of the missiles hit the building on Saturday. The Houthis in Yemen say they were behind the strikes and warned airlines and passengers against using Saudi Arabian airports and airspace. The group said they had targeted the airport with a mix of ballistic and cruise missiles, as well as drones. They also attacked oil facilities and Dammam airport in eastern Saudi Arabia, their military spokesman Brig Gen Yahya Saree said. He vowed to continue the "escalating operations deep inside Saudi Arabia", warning that all Saudi airports were potential targets apart from those in the holy cities of Mecca and Medina.