Tribal fighters loyal to the Yemeni government stand by a tank near Hodeida, Yemen, on June 1. (Reuters)

A Saudi Arabia-led military coalition and its local allies launched a long-anticipated offensive on the Yemeni port city of Hodeida early Wednesday, opening a new front in the country’s intractable civil conflict and raising fears for millions of civilians.

The offensive, which was announced by Yemen’s government, is aimed at dislodging an Iranian-allied rebel group known as the Houthis that controls Hodeida on Yemen’s Red Sea coast. The port is the main entry point for food and humanitarian aid supplies that millions rely on in Houthi- ­controlled areas.

The government and its Persian Gulf allies argue that defeating the Houthis in the city would force them to the negotiating table more than three years after they took over much of Yemen’s north, setting off a civil war and a devastating humanitarian crisis in the Arab world’s poorest country.

“The liberation of the port of Hodeida is a turning point in our struggle to take back Yemen from the militias that hijacked it,” a Yemeni government statement said, adding that the offensive “represents the beginning of the fall of the Houthis.”

Aid agencies have warned that the Hodeida offensive would almost certainly deepen civilian suffering, threatening nearly half a million people who live in the city while cutting off critical aid at a time when a third of Yemen’s citizens are on the brink of famine.

The United Nations had led an intensive diplomatic push to avert the offensive, which the Saudi-led coalition, and especially the United Arab Emirates, had long been determined to pursue.

Yemeni security officials quoted by the Associated Press said that 2,000 troops had crossed the Red Sea from a UAE naval base in Eritrea, with plans to seize the port at Hodeida. A separate ­Yemeni-UAE force was advancing from the south, near the city’s airport, the officials said.  

There were signs the rebels were intending to defend the city. Hazaa Alsilwi, a 25-year-old resident, said Houthis were mobilizing tanks and armored vehicles about 6 miles from the airport, which sits on the city’s southern edge.

 The Trump administration, which provides military support to the coalition, had asked the Emirates to hold off on an operation until after U.N. envoy Martin Griffiths presented a new plan for jump-starting peace talks.

 But once it became clear the Emirates would not hold back its allied Yemeni forces, U.S. officials said they were focused instead on trying to ensure that the operation did not damage key infrastructure, such as the port, and that civilian sites did not become targets. Officials also want to make sure aid is provided immediately. 

“Further military escalation will have serious consequences on the dire humanitarian situation in the country and will have an impact on my efforts to resume political negotiations to reach an inclusive political settlement to the conflict in Yemen,” Griffiths said in a statement. “I cannot overemphasize that there is no military solution to the conflict,” he said.  

Amanda Catanzano, the director for policy and advocacy at the International Rescue Committee, which operates in Yemen, said the fighting did not appear to have reached the city center on Wednesday. The port remained open, and a World Food Program ship had been able to offload supplies of grain, she said.

But any interruptions to the port’s operation, “even short ones, are catastrophic,” she said. “There is no give in this system.”  

On Tuesday, a bipartisan group of senators, including Bob Corker (R-Tenn.) and Robert Menendez (D-N.J.), the leaders of the Senate Foreign Relations Committee, wrote to Secretary of State Mike Pompeo and Defense Secretary Jim Mattis to express their “grave alarm” about circumstances in Hodeida. 

They said civilian harm and damage to the port were “unacceptable consequences for any responsible member of the community of nations.”

 The United States has provided military assistance to the Saudi-led coalition since it first intervened in Yemen’s civil conflict in March 2015. The support has continued despite international alarm over the coalition’s air campaign against the Houthis, which has killed thousands of civilians in airstrikes that human rights groups have alleged are frequently indiscriminate.

The Trump administration has become an increasingly vocal backer of the coalition, sharing its concerns about Iranian support for the Houthis and showing deference to close military partners such as the United Arab Emirates. UAE forces fight alongside U.S. Special Operations forces in a separate counterterrorism mission in Yemen focused on al-Qaeda in the Arabian Peninsula. 

U.S. officials, however, have been skeptical of coalition assertions that Iranian missiles are being smuggled to the Houthis through Hodeida’s port, which is subject to a U.N. inspections program.

At the same time, the Trump administration has been seeking ways to demonstrate a tough stance toward Tehran’s support of armed groups across the Middle East. Yemen, where Iran has provided only limited support for the Houthi movement, is seen as an easier starting point for that campaign than countries where Iran’s proxy support is more established. 

A statement by Pompeo on Monday about Hodeida appeared to signal that the United States was content to allow the Emirati-led offensive to proceed. “I have spoken with Emirati leaders and made clear our desire to address their security concerns while preserving the free flow of humanitarian aid and life-saving commercial imports,” it read.  

Speaking to reporters this week, Mattis said that U.S. support would continue at its current levels and suggested that U.S. aerial refueling, which lengthens flight times, increased the accuracy of Saudi and UAE bombing raids and so cut down on civilian casualties. 

Ryan reported from Washington.
Ali Al-Mujahed in Sanaa, Yemen, contributed,