According to a military source, the rebels have managed to seize a bit of territory
Fighting for the key Yemeni region of Marib has intensified, with 53 pro-government and Houthi rebel fighters dead in the past 24 hours, loyalist military officials said on Saturday.
The Houthis have been trying to seize oil-rich Marib, the government's last significant pocket of territory in the north, since February.
"The rebels have managed to seize a bit of territory" in the latest fighting northwest of the city, a pro-government military source said, adding that they did not threaten the city of Marib itself.
The same source said 22 government soldiers including five officers had been killed, along with 31 rebels.
The Houthis rarely announce casualties on their own side.
The Iran-backed rebels in 2014 overran the capital Sanaa, 120 kilometres to the west of Marib, along with much of northern Yemen.
That prompted a Saudi-led coalition to intervene the following year to prop up the government.
Loyalist military officials said on Saturday that coalition aircraft had carried out strikes against the rebels, but the Houthis had pushed on with their offensive.
The rebels have stepped up missile and drone strikes against neighbouring Saudi Arabia in recent months, rejecting a Saudi proposal for a ceasefire.
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 would also threaten a humanitarian disaster, as at least a million civilians displaced from fighting elsewhere have sought refuge in Marib camps.
The conflict in Yemen has killed tens of thousands of people and pushed millions to the brink of famine, according to aid agencies.
The United Nations says Yemen is suffering the world's worst humanitarian crisis.