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.

Yemeni military officials said to the Agence France-Presse (AFP) that the Houthis had advanced along two axes toward the city amid heavy fighting. The number of troops killed on both sides is expected to be in the hundreds. 

“The rebels have advanced north and west of the city… and tightened their grip on hills overlooking supply lines for several fronts,” one military source said to AFP.

Al Masirah, the Houthi television mouthpiece said that Saudi aircraft conducted 13 airstrikes, 11 on locations in the district of Sirwah and two in the district of Madghal. Marib had been mostly spared the violence that has plagued the country which is why it hosts nearly one million internally displaced persons. 

The United States called on the Houthis to stop the attack on Marib, cease all military operations, end cross-border strikes on Saudi Arabia and participate in an UN-led peace process. The attacks on Saudi Arabia have targeted civilian infrastructure and the Abha international airport according to the Saudis.

Just a week ago, the Biden administration revoked the foreign terrorist organization and specially designated global terrorist (SDGT) designations of the Houthi movement and pledged to bring humanitarian supplies to the people of Yemen. Biden also stopped all offensive support to Saudi Arabia, which has supported the government with troops and airstrikes.

Meanwhile, Iran and others are smuggling weapons into Yemen in support of the Houthi offensive.

Under the Obama administration, the U.S. had begun providing “logistical and intelligence support” to the Saudi-led coalition in March 2015, shortly after the Saudis and the United Arab Emirates (U.A.E.) had launched a military offensive in support of the overthrown President Abd-Rabbu Mansour Hadi.

The U.S. had created a joint U.S.-Saudi “planning cell” to coordinate military and intelligence assistance and in-air refueling of Saudi aircraft. Under Biden’s directive, the American intelligence support, regarding airstrikes will cease.

The UN considers the humanitarian situation in Yemen to be the worst in the world. 

State Department spokesman Ned Price said, “The Houthis’ assault on Marib is the action of a group not committed to peace or to ending the war afflicting the people of Yemen.”

Price called on the Houthis to “constructively participate” in UN-led peace efforts and “engage seriously” with the Biden-appointed U.S. special envoy for Yemen, Timothy Lenderking.

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Lenderking stated that Tehran “played a very negative role in Yemen” by financing, training, and supplying the Houthis in their attacks against civilian targets in Saudi Arabia and the Gulf. He called on Tehran to “put its best foot forward in terms supporting the kind of international response that we’re trying to engineer to end this conflict.” 

Although the Biden administration rewarded the Houthis by revoking the foreign terrorist designation in an attempt to jump-start the peace process and get humanitarian aid to the millions of people needing it, the Houthis and their advisors in Tehran have other plans. 

The Houthis won’t begin negotiations until they are in a position of strength: that includes taking the oil fields and continuing to attack civilian targets both in Yemen and Saudi Arabia. The Biden administration is in damage control over this development. According to Lenderking, “both [President Biden and Secretary Blinken] made clear we’re not going to allow Saudi Arabia to be target practice.”