Sanaa, Mar 8 (IANS): The UN has called for an immediate halt to fighting in northern Yemen where the Iran-aligned Houthi rebels seized control of a strategic city on the border with Saudi Arabia last week.

"I'm reiterating my call for an immediate and unconditional freeze and the start of a comprehensive, inclusive and accountable de-escalation process," Efe news quoted UN envoy to Yemen, Martin Griffiths, as saying in a tweet on Saturday.

He made the remarks during a first visit to Marib city, the capital of the oil-rich Marib province, the bastion of government military forces backed by the Saudi-led coalition.

Marib is located near al-Hazm city, capital of the province of Al Jauf and border with Saudi Arabia, which was seized last March 1 by Yemeni rebels after weeks of fighting against government forces.

"Yemen is at a critical juncture; it will either silence the guns and resume the political process, or we will slip back into large-scale conflict," Griffiths said following meetings with government officials in Marib city, around 195 km northeast of the rebel-held capital of Sanaa.

The seizure of the city dealt a big blow to the internationally-recognized government of President Abd Rabbuh Mansour Hadi and the coalition, as it brings the rebels closer to Marib.

"Marib has been a haven for hundreds of thousands of displaced Yemenis. Just last week, thousands of families arrived here fleeing fighting in al-Jawf. The parties need to ensure that Marib will remain a haven, not the next epicenter of the war," Griffiths said.

"Military adventurism and the quest for territorial gains are futile," he added in reference to the Houthis.

Yemen has been gripped in a power struggle between the Saudi-backed government and the Houthi rebels since late 2014.

The conflict intensified when Saudi Arabia began a military intervention in Yemen in March 2015 in support of Hadi against the Houthi rebels, leaving 24 million people in need of humanitarian aid, according to the UN.