The rebels have accelerated their push to take Marib in recent months, while escalating cross-border attacks on Saudi Arabia, which leads the military coalition opposing them.
Fighting has flared up between Yemen's pro-government forces and Houthi rebels in the oil-rich government stronghold of Marib province, with at least 28 fighters killed over the last 24 hours, security officials from both sides and tribal leaders said.
Most of the fatalities were among the Iran-backed rebels assaulting the city of Rahbah, said the officials on Thursday.
Thousands of fighters — mostly Houthis — have died in the Marib offensive, with 12 government troops killed on Monday.
Since then, fighting has intensified in Rahbah, which had been under Houthi control for almost two years before falling to government troops in July.
Meanwhile, the Saudi-led coalition has launched dozens of airstrikes on cities in Marib — including Rahbah, Sirwah and Madghel — to back pro-government ground forces, according to the Houthi media centre.
Yemen’s civil war began in 2014 when the Houthis seized Sanaa and much of the north, forcing the government of President Abd Rabbu Mansour Hadi to flee.
The Saudi-led coalition, backed at the time by the U.S., entered the war to try to restore Hadi to power. A relentless air campaign and ground fighting has killed more than 130,000 people and spawned the world’s worst humanitarian crisis.
It has also created smaller, parallel conflicts, between militants and different factions inside the country.
On Sunday, a missile and drone attack on a key military base in Yemen’s south killed at least 30 troops, a Yemeni military spokesman said.
It was one of the deadliest attacks in the country’s civil war in recent years. At least 64 people were wounded in the attack on on Al Anad air base in the province of Lahj. No one immediately claimed responsibility for the attack.