CAIRO — More than 70 people were wounded in a wave of Houthi attacks Tuesday on Saudi Arabia, authorities said, a major escalation in the renewed conflict between an important U.S. ally and the Iranian-backed rebels in Yemen.

The attacks come after weeks of escalating clashes between the Houthis and Saudi-backed government forces in Yemen, which shattered a four-year truce in the country’s civil war.

Fighting has raged on fronts including Yemen’s west coast, with government forces saying they have made territorial gains in the provinces of Hodeida, Taiz and Baydah. The Houthi have also launched attacks on Saudi oil facilities and tankers in the Red Sea.

The attacks early Tuesday hit “civilian and economic facilities” in the Saudi cities of Abha’s Jazan, Najran and Khamis Mushait said Maj. Gen. Turki al-Malki, a spokesperson for the Saudi-led coalition fighting in Yemen, said in a statement.

Al-Malki said the attacks wounded 73 people, including women and children. He didn’t provide a breakdown or further details.

He called the attacks a “serious escalation” and a “flagrant violation of the kingdom’s sovereignty, and a direct threat to the security and safety of its citizens and residents.”

Al-Malki vowed retaliation, saying that the Saudi-led coalition “will take all necessary operational measures to deter the terrorist Houthi militia with utmost resolve.”

There was no immediate comment from the Houthis.

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

Yemen’s civil war began in 2014 when the Houthis seized the capital, Sanaa, and much of northern Yemen and forced the government into exile.

A Saudi-led coalition, including the United Arab Emirates, intervened the following year to try to restore the government to power.

Tensions rose earlier this year between U.S. allies Saudi Arabia and the UAE as their partnership in the war in Yemen broke down, leading to the UAE pulling out of Yemen.

The civil war in Yemen has killed at least 150,000 people, according to U.N. estimates, and at times pushed the country to the brink of famine.