More than 70 people were wounded Tuesday in a series of Houthi attacks on Saudi Arabia, according to authorities. The strikes, which hit civilian and economic facilities in the cities of Abha, Jazan, Najran, and Khamis Mushait, represent a significant escalation in the conflict between Saudi Arabia and the Iranian-backed rebels in Yemen.

Maj. Gen. Turki al-Malki, a spokesperson for the Saudi-led coalition fighting in Yemen, described the attacks as a "serious escalation" and a "flagrant violation of the kingdom's sovereignty." He vowed that the coalition "will take all necessary operational measures to deter the terrorist Houthi militia with utmost resolve."

Al-Malki stated that the attacks wounded 73 people, including women and children, though he did not provide a further breakdown of the casualties.

The attacks occurred after weeks of intensified clashes between the Houthis and Saudi-backed government forces in Yemen, which shattered a four-year truce. Government forces have reported territorial gains on fronts including the west coast, in the provinces of Hodeida, Taiz, and Baydah. The Houthis have also targeted Saudi oil facilities and tankers in the Red Sea.

The strikes also came hours after the Houthis blamed Saudi Arabia for an airstrike that hit a prison in Yemen’s northern Jawf province. At least seven people, including a child, were killed and seven others were wounded in that strike, the rebels said.

Yemen's civil war began in 2014 when the Houthis seized the capital, Sanaa, and other parts of northern Yemen, forcing the government into exile. A Saudi-led coalition intervened in 2015 to support the Yemeni government.

Past U.N. estimates indicate the civil war has killed at least 150,000 people and at times brought the country to the brink of famine.