The Yemeni government said on Saturday that the Houthi militias are using civilians as human shields in their renewed offensive in the city of Marib.
Earlier this month, the Iran-backed militias resumed a push to capture the city, which is 120 kilometres (75 miles) east of the capital Sanaa.
The city lies close to some of Yemen's richest oil fields. However, the fighting has raised fears for the hundreds of thousands of displaced civilians sheltering in camps in the surrounding desert that extends to the Saudi border.
Two military officials told AFP the Houthis had been using residents of Al-Zor camp in the province's Sirwah district as "human shields" since their capture of the area last week.
The officials said there had been no let-up in the fighting.
Over the past 24 hours, at least 12 loyalists and 20 Houthis had been killed in clashes north and west of Marib, they said.
Until early last year, Marib had been spared the worst of the civil war that erupted in 2014.
The International Committee of the Red Cross has said it is "extremely concerned" by the recent fighting.
"The ICRC urges all parties to the conflict to take every possible measure to protect the civilians, their properties and all civilian essential infrastructures," it said on Twitter.
The UN has warned of the potential for a humanitarian disaster.
"It puts millions of civilians at risk, especially with the fighting reaching camps for internally displaced persons," envoy Martin Griffiths told the UN Security Council.
Observers say the Houthis want to capture Marib to strengthen their hand in eventual peace negotiations.