ADEN (Reuters) - Arab coalition aircraft bombarded Houthi fighters dug in at the airport of Yemen’s main port Hodeidah on Monday as a senior alliance official said he hoped U.N. diplomacy could coax the Iran-aligned movement to cede the city to “save the population”.

Children stand behind a fence at a school to which they have been evacuated from a village near Hodeidah airport amid fighting between government forces and Houthi fighters in Hodeidah, Yemen June 17, 2018. REUTERS/Abduljabbar Zeyad

U.N. officials fear a prolonged battle for Hodeidah, where the Houthis are dug in to protect supply lines from the Red Sea to their bastion in the capital Sanaa, will aggravate what is already the world’s most urgent humanitarian crisis.

The Western-backed Arab alliance launched an onslaught on Hodeidah six days ago in order to turn the tables in a long- stalemated proxy war between Saudi Arabia and Iran that has compounded instability across the Middle East.

The coalition intervened in Yemen’s war in 2015 after Houthi rebels drove the internationally recognized government into exile. United Arab Emirates forces are spearheading the Hodeidah offensive, now focused on the airport of the Red Sea city.

On Monday Apache helicopter gunships fired at Houthi snipers and other fighters positioned on the rooftops of schools and homes in the Manzar neighborhood abutting the airport compound, according to local residents.

Houthi forces had blocked roads to the airport, they said.

The Houthis’ al-Masira television reported six coalition air strikes on the Duraihmi district in the vicinity of the port.

The upsurge in fighting has wounded dozens of civilians and prevented aid organizations from reaching parts of Hodeidah.

In Geneva, U.N. human rights chief Zeid Ra’ad al-Hussein voiced concern that the Arab offensive could cause “enormous civilian casualties and have a disastrous impact on life-saving aid to millions of people which comes through the port”.

The United Nations says 22 million Yemenis depend on aid, and 8.4 million are on the verge of starvation. For most, the port of Hodeidah is the only lifeline.

The Arab alliance says it can take Hodeidah quickly enough to avoid interrupting aid. But it has never before tried to capture such a heavily defended city, and there are fears the battle could drag on.

Yehia Tanani said he and his family left Manzar three days ago and walked for 3 km (1.86 miles), hiding behind walls and under trees to avoid air raids before sheltering at a fish farm.

“They told us that some humanitarian organizations are going to send buses but then they said no buses could come in or out. So we started walking on foot carrying our children, sitting every while for rest while the Apaches hovered above us. We were scared not knowing if we’d be shot or not,” Tanani said.

“Now we’re in this school, no mattresses, no electricity, no water, no bathrooms, nothing. And we have children who need medicine, need food, need anything, but we don’t have anything,” he said in a classroom used to house displaced people.

UAE Minister of State for Foreign Affairs Anwar Gargash told a news conference in Dubai that the coalition was taking a measured approach to minimize risks to civilians, and allowing the Houthis an escape route inland to Sanaa.

One hundred trucks of food aid were en route to Hodeidah on the road from coalition-controlled Aden and Mokha to the south.

“METHODICAL” OFFENSIVE

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“We have planned diligently around the humanitarian challenge,” he said. “Our approach is methodical, gradual, calibrated to squeeze, to make a point, to allow the Houthis to do the right thing, which is basically decide to withdraw unconditionally.”

He said the coalition was counting on Martin Griffiths, the U.N. special envoy for Yemen, to secure a Houthi agreement to vacate Hodeidah.

Griffiths returned to Sanaa on Saturday for talks. Houthi authorities and the United Nations office in Sanaa said he would stay until Tuesday, after originally saying he would depart on Monday, hinting at possible progress.

Arab coalition spokesman Turki al-Malki said Griffiths was trying to find political solutions amid Houthi “intransigence over handing over Hodeidah city and port”. Houthi officials in Sanaa could not immediately be reached for comment.

Iranian President Hassan Rouhani said on Monday that fresh military action would not resolve Yemen’s crisis.

“The crisis in Yemen should be resolved through political channels...A military approach will fail,” Rouhani told Qatari Emir Sheikh Tamim bin Hamad al-Thani in a phone call, reported by Iranian state television.

“We regard as incorrect the adventurous policies of certain regional countries and believe that the continuation of this process will undoubtedly intensify the existing regional crisis,” Rouhani said.

The Houthis, who rule Yemen’s capital and most of the populated areas in the unstable nation of 30 million people, deny the Arab states’ assertions they are puppets of Iran. They say they came to power in a popular revolt against corruption and are protecting the country from foreign invasion.

Gargash estimated the number of Houthi fighters in Hodeidah at between 2,000 to 3,000. He described them as “militia, non-descript, not in uniform”, with battlefield tactics revolving around sniper fire and mine-laying.