Iranian-supplied and led Houthi rebels in Yemen have started an offensive against the oil-rich Marib province located about 75 miles east of the rebel-held capital of Sanaa.

The offensive by the Houthis, if successful, would be a huge blow to the internationally recognized government of Yemen, and deprive it of its last stronghold in the northern part of the country. 

Mark Lowcock, the UN undersecretary-general for humanitarian affairs, posted on Twitter that an assault on Marib could endanger two million civilians and cause hundreds of thousands to flee the city, which would have “unimaginable humanitarian consequences.”

“Now is the time to de-escalate, not to add even more to the misery of the Yemeni people,” Lowcock added.