ADEN/DUBAI (Reuters) - Thousands of Yemeni civilians are trapped on the southern outskirts of the Red Sea port of Hodeidah as forces backed by a Saudi-led coalition battle Houthi insurgents entrenched in the city, aid groups said on Monday.

The alliance has massed thousands of Yemeni troops in recent days near the heavily defended port, but a source in the coalition told Reuters there were no immediate plans for an assault.

The United Nations has said an attack on the city, entry point for 80 percent of impoverished Yemen’s food imports and relief supplies, would risk triggering a famine.

The fighting has reached populated areas around a university 4 km (2.5 miles) from the port and has come close to the main hospital for the first time, aid groups and residents said.

“All the people living between the airport and the university are trapped, the last four days have been very tough, it is beyond catastrophic levels,” said Isaac Ooko, Hodeidah area manager for the Norwegian Refugee Council (NRC).

“Air strikes have been very intense and the hovering of the jets causes permanent anxiety ... Hodeidah has become a ghost city, people stay indoors and the streets are deserted,” he told Reuters by telephone.

Juliette Touma, spokeswoman for the U.N. children’s fund UNICEF who was recently in Hodeidah, voiced fears for al-Thawra, the main hospital on Yemen’s western coast and a center of cholera and diphtheria treatment.

“You could hear the fighting from the hospital and from our guest house close to it,” she said.

CEASEFIRE CALLS

Capturing Hodeidah would allow the Saudi-led coalition to cut off the main supply line of the Iranian-aligned Houthis, who control most of northern Yemen, including the capital Sanaa.

Bandar al-Aiban, head of the official Saudi national human rights commission, told the U.N. Human Rights Council in Geneva that coalition forces were “doing their best to spare civilians, particularly women and children, civilian sites, and infrastructure as a side-effect of the armed conflict”.

Western countries have called for a ceasefire to support efforts to end a war that has lasted more than three years and killed more than 10,000 people.

Saudi Arabia and the United Arab Emirates have not publicly commented on those calls, but the coalition source said the military deployment aimed to put pressure on the Houthis to return to negotiations. U.N.-led talks in Geneva fell apart in September after the Houthis failed to show up.

The Sunni Muslim coalition led by Saudi Arabia and the UAE intervened in Yemen in 2015 to try to restore the internationally recognized government of President Abd-Rabbu Mansour Hadi and has been under growing international scrutiny over civilian deaths.

It relies heavily on Western arms and intelligence in the conflict, widely seen as a proxy war between Saudi Arabia and Iran.

But its relationship with key Western allies has been badly strained by the murder of prominent journalist Jamal Khashoggi in the Saudi consulate in Istanbul last month.