Earlier on Sunday, Abdul Malik al-Houthi, the leader of Yemen's Houthi rebels, vowed to "use long-range weaponry" and "recruit more fighters" in the conflict with his northern neighbour.

"In the fourth year of the war, we will use more developed and more diverse missile systems which will overcome all American and non-American air defence systems to target Saudi Arabia," al-Houthi said in a lengthy televised speech.

"We'll use our Badr [short-range ballistic missiles] and Burkan missiles, long range drones which have excellent military capabilities. We will activate military institutions in an unprecedented way and open up more opportunities to recruit the children and men of our people to fight."