ADEN (Reuters) - Forces from an alliance of Arab states seized two entrances to the airport in Yemen’s main port city on Friday, in an offensive against the Iran-aligned Houthi movement that the United Nations fears could trigger a famine imperiling millions of lives.

The swift advance was an important early success for the Saudi- and United Arab Emirates-led alliance, which launched the operation in Hodeidah three days ago and says it can seize the city quickly enough to avoid interrupting aid to the millions facing starvation.

“We saw the resistance forces in the square at the northwestern entrance to the airport,” said a Hodeidah resident, referring to Yemeni allies of the Saudi-led coalition. Two Yemeni military officials allied to the coalition confirmed this.

Alliance-backed Yemeni forces tweeted that they had also seized the airport’s southern entrance and were advancing down a main road toward the Hodeidah seaport.

The UAE state news agency said Houthi fighters at the airport were crumbling. However, local military sources said the Houthis have surrounded themselves with a large number of landmines, meaning that it would take some time for coalition forces to battle their way to the main airport buildings.

Residents said battles had been fought in the Manzar neighborhood abutting the wall around the airport. “There have been terrifying bombing runs since the morning when they struck Houthi positions near the airport,” said fish vendor Ammar Ahmed. “We live days of terror that we have never known before.”

In the evening, a first ambulance made it into the area and evacuated seven wounded civilians, but two of them died before reaching hospital, a medical source told Reuters.

Apache attack helicopters hovered over Manzar, firing at Houthi snipers and fighters in schools and other buildings, said another resident, who asked not to be identified. Houthi forces had entered homes overlooking the main road to go onto the roofs.

Streets elsewhere in the city were empty despite the Eid holiday marking the end of the Ramadan fast. Houthi fighters amassed in the city center where a hospital put out a call for blood donations, the resident said.

Aid agency CARE International quoted its last staff member in Hodeidah as saying: “The situation is very scary, scarier than it has ever been before. We can hear the fighting coming close and the situation is really changing for the worse.”

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BIG GAMBLE

The coalition of Arab states has battled with little success for three years to defeat the Houthis, who control the capital Sanaa, the Hodeidah port and most of Yemen’s populated areas. The assault on Hodeidah is the alliance’s first attempt to capture such a well-defended major city.

“We are at the edges of the airport and are working to secure it now,” the Arab coalition said in a statement to Reuters. “Operational priority is to avoid civilian casualties, maintain the flow of humanitarian aid, and allow for the UN to press the Houthis to evacuate the city.”

The assault is a gamble by the Arab states, who insist they can swiftly capture the port without major disruption to aid supplies in a country already experiencing the world’s most pressing humanitarian crisis.

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The United Nations, which struggled but failed to find a diplomatic path to head off the assault, fears the fighting will cut off the only lifeline for most Yemenis. Around 22 million depend on aid and 8.4 million are at immediate risk of starvation.

Western countries have long given the Arab states tacit diplomatic backing and sell them billions of dollars a year in arms. But that support could falter if the assault provokes the feared humanitarian catastrophe.

“I urge all parties to the conflict to meet their obligations to protect civilians and civilian infrastructure and take active steps to respect international humanitarian law,” said David Beasley, head of the U.N. World Food Programme.

The U.N. Special Envoy to Yemen, Martin Griffiths, is due to arrive in Sanaa on Saturday.

Capturing Hodeidah would give the Arab coalition the upper hand in the war, in which it has fought since 2015 to restore an exiled government driven out by the Houthis. But a successful operation would require capturing a city of 600,000 people without inflicting damage that would destroy the port.

Civilians are fleeing if they have anywhere to go, or staying and bracing for a battle.

“My family left for Sanaa yesterday but I stayed behind alone to protect our home from looters,” said Mohammed Abdullah, an employee of the Houthi administration.

Riyadh and Abu Dhabi say the Houthis are a proxy force for Iran, their regional arch-rival. The Houthis, from a Shi’ite minority, deny being Tehran’s pawns. Instead, they say they took power in a popular revolt and are defending Yemen from invasion by its neighbors.