NEHIM, Yemen — Desperate to break through enemy lines, the Saudi-backed forces fighting in Yemen are sending untrained soldiers to clear minefields, sometimes using only their bayonets.

“I removed two and the third one exploded,” said Sultan Hamad, a 39-year-old Yemeni soldier who lost a leg clearing mines on the front line near Marib, an ancient city in central Yemen. He was among more than a half dozen soldiers waiting at a clinic in Marib to be fitted for prosthetic limbs.

Nearly four years after Saudi Arabia plunged into Yemen’s civil war, Saudi and Yemeni commanders say that hundreds of thousands of unmarked land mines planted by their opponents, the Houthis, have emerged as perhaps their most formidable defense.

The hidden explosives, the commanders say, have helped keep the conflict close to a standstill despite the superior air power and other resources of the Saudi-led coalition.