Dubai - At least 31 people were killed in air strikes on Yemen Saturday, the United Nations said. The Tornado aircraft came down Friday in northern Al-Jawf province during an operation to support government forces, a rare shooting down that prompted operations.

The deadly violence follows an upsurge in fighting in northern Yemen between the warring parties that threatens to worsen the war-battered country's humanitarian crisis.

"Preliminary field reports indicate that on 15 February as many as 31 civilians were killed and 12 others injured in strikes. Lise Grande, the UN coordinator, denounced the "terrible strikes". "Under international humanitarian law, parties which resort to force are obligated to protect civilians," she said. "Five years into this conflict and belligerents are still failing to uphold this responsibility. It's shocking."

The militants reported multiple coalition air strikes in the area where the plane went down, adding that women and children were among the dead and wounded, according to television station Al-Masirah.

The coalition conceded the "possibility of collateral damage" during a "search and rescue operation" at the site of the jet crash, which left the fate of its crew uncertain.