Heavy fighting has raged in Yemen's civil war, extending a week of violence between forces of the country's internationally recognised government and Houthi rebels.
With dozens killed, the fighting in the strategic province of Marib has cast major doubt over UN-led efforts to restart negotiations to end years of war.
The Iranian-backed rebels earlier this month renewed their attack on the oil-rich province, an anti-Houthi stronghold held by the internationally recognised government.
But they faced stiff resistance and have not made progress amid heavy causalities mostly from the Houthis, military officials from both sides said.
Yemen's war started in 2014, when the rebels seized the capital Sanaa and much of the country's north. A Saudi-led, US-backed team intervened months later to dislodge the Houthis.
The conflict has killed some 130,000 people and spawned the world's worst humanitarian disaster.
The rebels seek to wrestle control of Marib, closing off Saudi-Arabia's southern border and taking control of oil fields in the province that would give them leverage in possible peace negotiations.
Alarmed by the Houthis' renewed push, the Saudi-led coalition bombed the advancing convoys in the sprawling desert around Marib.
It also brought in ground enforcements from the government-held provinces of Taiz and Shabwa, the officials said.
The Houthis' media office reported on Tuesday at least 10 airstrikes by the Saudi-led coalition in Marib, and two more airstrikes on the neighbouring province of Jaw, which the rebels use as base to launch their latest attack in Marib.
More than 48 fighters were killed and over 120 were wounded in the past two days, mostly Houthis, officials said.
Over two dozen others were reported killed at the start of the attack, which has mostly centred in the districts of Sorouh and Makhdara, they added.
The rebels have been marching towards Marib since the beginning of 2020, attacking the city from several sides and putting a burgeoning civilian population at risk.
The province, which houses the ancient Great Marib Dam, has served as a sort of haven for hundreds of thousands of Yemenis who have fled Houthi offensives since the start of the war.
The fighting in Marib could also thwart renewed efforts by the UN to re-launch negotiations between the warring sides. They have not held substantive negotiations since 2019.
UN envoy Martin Griffiths said last week he was "extremely concerned" about hostilities in Marib.
US President Joe Biden has turned a spotlight on the brutal conflict, declaring earlier this month that the US would end its support of the Saudi-led military offensive, including "relevant" arms sales.