Yemen's Iran-backed Huthi rebels have made major advances on Marib city after taking a strategic mountain in clashes that caused dozens of casualties on both sides, government sources said Friday.
The Huthis and the internationally recognised government have been locked in a power struggle since 2014, when the rebels overran the Yemeni capital Sanaa.
Since last month, the rebels have been pushing to seize Marib, the government's last northern stronghold and the capital of an oil-rich region.
The Huthis "took control of Mount Hilan overlooking the city, after fighting which left dozens of dead and wounded on both sides," one of the sources told AFP.
"Marib is in danger," another source said, adding the loss of the mountain posed "a threat to Marib's first line of defence".
The loss of Marib would be a huge blow for the Yemeni government, but would also threaten catastrophe for civilians, including at least one million displaced people sheltering in the region, many in desolate camps in the surrounding desert.
The Huthis had "cut the supply lines of some fronts and are now within firing range of the Al-Mashjab line west of Marib city," the source added.
Despite the advance, analysts say the city may not fall to the rebels any time soon, given the overwhelming firepower of the Saudi-led military coalition which backs the beleaguered government.
"An imminent fall of Marib remains unlikely," Maged Al-Madhaji of the Sanaa Center think tank told AFP, adding that this was nonetheless "an important advance that puts additional pressure" on government forces.
The Saudi-led military coalition intervened in the conflict in 2015, enforcing a naval and air blockade to prevent the smuggling of weapons to the rebels from Iran -- allegations Tehran denies.
The rebels say any ceasefire agreement can only begin after the Saudi-led blockade of Yemen is lifted.
- Million at 'grave risk' -
The news of their advance came just hours after the United Nations Security Council condemned the "escalation" of armed clashes around Marib city and warned of a worsening humanitarian catastrophe.
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," it said.
It "stressed the need for de-escalation by all, including an immediate end to the Huthi escalation in Marib (and) condemned the use of child soldiers in Marib."
Life in the city retains a veneer of normality despite the conflict that rages outside, but there is a sense of dread as the fighting draws nearer.
"We condemn what is happening to the city of Marib. Our children are terrified," one resident, Um Ali, told AFP.
Another resident, Mohammed Yahya, said the city would "remain steadfast".
"This is what history told us -- that, throughout the ages, Marib has been the thorn that breaks down any enemy that wants any harm to Yemen," he said.
Tens of thousands of people, mostly civilians, have been killed and millions displaced in Yemen's long war, which has crippled the economy and healthcare system. The UN has declared Yemen the world's worst humanitarian crisis.
The United States has sought to revive stalled peace talks since Joe Biden took over from Donald Trump as president in January.
In a bid to get the rebels to the negotiating table, Washington has withdrawn support for the coalition's offensive in Yemen and swung its diplomatic clout behind the UN pointman on Yemen, Martin Griffiths, whose job it is to revive the peace process.
Madhaji said the Huthis view the battle for Marib as an "essential and decisive" confrontation and see the negotiations only as a last option if they fail to take the city.
"If the Huthis take over Marib, there is no chance for peace in the near future in Yemen, at least for the next three to four years," the analyst said.