Two officials from pro-government forces say that the rebels were mounting a concerted push that had left 26 loyalist soldiers dead as well as 44 from Houthi ranks.
Fierce fighting for Yemen's strategic Marib city has killed 70 pro-government and Houthi rebel fighters over the past 24 hours, with battles raging on three fronts, according to loyalist military officials.
The Houthis have been trying to seize Marib, the capital of an oil-rich region and the government's last significant pocket of territory in the north, since February.
Two officials from pro-government forces told AFP that the rebels were mounting a concerted push that had left 26 loyalist soldiers dead as well as 44 from Houthi ranks. The rebels rarely disclose their losses.
The new toll adds to 53 killed on both sides in the previous 24 hours, according to loyalist military officials.
One of the officials said on Sunday that the rebels "are launching simultaneous attacks" in the areas of Kassara and Al Mashjah, northwest of the city, and Jabal Murad in the south.
"They have made progress on the Kassara and Al Mashjah fronts, but they have been thwarted on the Jabal Murad front," he told AFP.
The other official said that warplanes from the Saudi-led military coalition, which entered the Yemen conflict to support the government in 2015, launched air strikes that "destroyed 12 Houthi military vehicles, including four tanks and a cannon."
However, the Saudi firepower does not seem to have halted the rebel offensive.
Fears for civilians
The Iran-backed Houthis in late 2014 overran the capital Sanaa, 120 kilometres (75 miles) to the west of Marib, along with much of northern Yemen.
The loss of Marib would be a heavy blow for the Yemeni government, currently based in the southern city of Aden, and for its Saudi backers.
It could also lead to humanitarian disaster, as vast numbers of civilians displaced from fighting elsewhere have sought refuge in Marib.
Around 140 sites have sprung up in the region to provide basic shelter for up to two million displaced, according to Yemen's government.
The rebels have stepped up missile and drone strikes against neighbouring Saudi Arabia in recent months, demanding the opening of Yemen's airspace and ports. They have rejected a Saudi proposal for a ceasefire.
UN warns of a looming humanitarian disaster
The United Nations last month condemned the escalation and warned of a looming humanitarian disaster.
The UN Security Council said the fighting "places one million internally displaced persons at grave risk and threatens efforts to secure a political settlement when the international community is increasingly united to end the conflict".
US Secretary of State Antony Blinken has warned that the suffering will only end when a political solution is found between the Houthis and the internationally recognised government.
The conflict in Yemen has killed tens of thousands of people and pushed millions to the brink of famine, in what the the United Nations has described as the world's worst humanitarian crisis.