RIYADH, Aug. 9 (Xinhua) -- The Saudi-led coalition on Thursday defended the airstrike targeting Yemen's Saada governorate as "legitimate" response to a deadly Houthi attack on the Saudi border city Jazan.

The coalition targeted the militants who planned and carried out the attack against Jazan on Wednesday, coalition spokesperson Turki Al-Maliki was quoted by the official Saudi Press Agency as saying.

Maliki added that the coalition strike was a "legitimate military action," which was conducted in conformity with the international law.

He warned that the coalition would take all steps against "terrorist and criminal acts" of Iranian-backed Houthi militias, such as using underage soldiers as tools in their "terrorist acts."

The spokesperson affirmed that the militants responsible for launching missiles and targeting civilians will be held accountable under the coalition's efforts to prevent "terrorist elements" from compromising regional and international security.

Meanwhile, the head of Yemen's Saada Health Office, Yahya Shayem, told Xinhua that at least 43 people were killed earlier Thursday as the Saudi-led coalition airstrike hit the buses carrying school pupils "on their way to attend a summer school in Dhahyan."

Saudi Arabia has been leading an Arab coalition to fight the Houthi rebels, who control Yemen's north, with airstrikes in the last three years, while the Houthi militias often respond with launching missiles at Saudi border cities.