A series of Houthi attacks targeting Saudi Arabia on Tuesday left 73 people injured, according to Saudi authorities, marking a significant escalation in the renewed hostilities involving the U.S.-allied kingdom and the Iran-supported Houthi movement in Yemen.

The latest attacks followed several weeks of intensified fighting between Houthi forces and troops supporting Yemen’s Saudi-backed government. The violence brought an end to a four-year period of relative calm in the country’s long-running civil war.

Battles have intensified across several areas of Yemen, including the western coastline. Government forces have claimed recent advances in Hodeida, Taiz and Baydah provinces. Meanwhile, the Houthis have continued targeting Saudi oil infrastructure and vessels operating in the Red Sea.

Maj. Gen. Turki al-Malki, spokesperson for the Saudi-led coalition involved in the Yemen conflict, said the early Tuesday attacks struck civilian and economic sites in the Saudi cities of Abha, Jazan, Najran and Khamis Mushait.

According to al-Malki, 73 people were injured, among them women and children. He did not release further information about the victims or explain how many were wounded at each location.

Al-Malki described the strikes as a major escalation and accused the Houthis of violating Saudi Arabia’s sovereignty and endangering the security of people living in the kingdom. He also warned that the coalition would respond.