SANAA, Yemen (AP) — The Saudi-led military coalition fighting in Yemen stepped up its bombing campaign Tuesday, launching airstrikes near the rebel-held capital in clashes that killed at least 35 people, Yemeni security officials said.

It was the first time in months that coalition airstrikes hit Houthi targets in the district of Nehm, some 60 kilometers (37 miles) northeast of the capital Sanaa, said Houthi officials.

The officials spoke on condition of anonymity in line with regulations..

Throughout the day, both sides fired rockets and pounded the area with artillery. The heavy fighting killed and wounded dozens, and forced scores of families to flee. The number of civilian casualties was not immediately known. Video provided by Yemen’s defense ministry showed large plumes of smoke rising over the mountains after the airstrikes.

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Abdu Abdullah Magli, spokesman for the Yemeni Armed Forces, said the army made major progress on the ground, seizing several strategic roads and Houthi sites. The Houthis reinforced their outposts and deployed new troops to the front.

Meanwhile, coalition warplanes also bombed rebel targets west of the Marib province, killing several Houthi fighters and capturing over 25, according to Yemeni military officials. The Houthi faction declined to comment.

Magli said the wave of bombings comes in retaliation for a Houthi missile attack on a mosque in Marib that killed at least 116 Yemeni government troops over the weekend. The death toll ranked among the highest from a single rebel assault since the start of the war, sparking widespread condemnation. U.S. and U.N. officials warned that the military escalation could undermine peace efforts.

Yemen’s civil war erupted in 2014 when Iran-backed Shiite Houthi rebels seized Sanaa, along with much of the country’s north, ousting President Abed Rabbo Mansour Hadi. Months later the Saudi-led Arab coalition intervened to try and restore Hadi’s internationally recognized government.

The regional proxy war has dragged on for years, killing more than 10,000 people, displacing over 3 million and pushing the country to the brink of famine. Fighting has settled into a bloody stalemate.

International efforts to end the war have made little progress. Yet in recent months, Saudi Arabia started backchannel negotiations with the Houthis in Oman after the rebels claimed an attack on Saudi oil infrastructure that threatened global oil supplies. The United States blamed the attack on Iran, which denied involvement.