CAIRO (Reuters) - A Saudi-led coalition fighting Yemen’s Houthis intercepted and destroyed six ballistic missiles fired by the Iran-aligned group targeting civilians in Jizan, southwest of the kingdom, Saudi state news agency SPA said on Sunday.

Earlier, the military spokesman for the Iran-aligned Houthi movement said the group fired 10 Badr-1 ballistic missiles at Saudi Arabia’s southwestern Jizan airport, adding that the attack had killed and wounded dozens.

The attack is part of an escalation of cross-border assaults in the four-year-old conflict between the Houthis and coalition forces.

The Houthis, who control the capital Sanaa, have in the past few months stepped up their attacks against targets in the kingdom. In response, the coalition has targeted military sites belonging to the group, especially around Sanaa.

“The Houthi militias continued targeting of civilians through drones and ballistic missiles ...is an act of aggression and terrorism and a war crime according to international human law,” the coalition spokesman, Colonel Turki al-Malki, said in a statement.

The Western-backed Sunni Muslim coalition led by Saudi Arabia and the UAE intervened in Yemen in 2015 to try to restore the internationally recognised Yemeni government that was ousted from power in Sanaa by the Houthis in late 2014.

The escalation of violence threatens a U.N.-sponsored deal for a ceasefire and troop withdrawal from Hodeidah, which became the focus of the war last year when the coalition tried to seize the port, the Houthis’ main supply line and a lifeline for millions of Yemenis.