The State Department’s comments came the same day that the revocation of the Houthis’ status as a terrorist group took effect. The move by President Joe Biden’s administration was welcomed by the U.N. and aid groups who feared former president Donald Trump’s actions would impede aid deliveries to the country.

Yemen’s war started in 2014 when the Iran-backed Houthis seized the capital, Sanaa, and much of the country’s north. A Saudi-led, U.S.-backed coalition intervened months later to dislodge the rebels and restore the internationally recognized government. The conflict has killed some 130,000 people and spawned the world’s worst humanitarian disaster.

The rebels earlier this month renewed their attacks on the oil-rich province, an anti-Houthi stronghold. However, they have faced stiff resistance and have not made progress amid heavy air bombing from the Saudi-led coalition.

The latest bout of violence killed dozens of fighters, mostly among the Houthis, and sparked fears of a new humanitarian crisis.

Marib province, the location of the ancient Great Marib Dam, has served as a sort of haven for around 1 million Yemenis who have fled Houthi offensives since the start of the war, the State Department said, citing U.N. figures.

“An assault on the city would put two million civilians at risk, with hundreds of thousands potentially forced to flee — with unimaginable humanitarian consequences,” U.N. Humanitarian Chief Mark Lowcock tweeted Monday.

Price, the state department spokesperson, also called on the Houthis to stop their cross-border attacks on Saudi Arabia.

The rebels have recently intensified attacks using explosive-laden drones and missiles on the kingdom in an apparent attempt to pressure the Saudi-led coalition to stop its air campaign against the rebels in Marib and elsewhere in Yemen.

Despite removing the terrorist designation from the Houthis, U.S. Secretary of State Antony Blinken noted last week that rebel leaders remain under U.S. sanctions. He said the Biden administration was “actively identifying additional targets for designation, especially those responsible for explosive boat attacks against commercial shipping in the Red Sea” and drone and missile attacks on to Saudi Arabia.

Price also urged the Houthis to engage “constructively” and “seriously” in efforts by envoys from the U.N. and the U.S. that aim to find a settlement to the conflict.

“The time to end this conflict is now. There is no military solution,” he said.

In an apparent response to the U.S. statement, Mohamed Abdel Salam, a Houthi spokesman, called for the Saudi-led coalition to end its campaign and lift the blockade on Houthi-held areas.

After that, “we are ready to engage positively,” he said.

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