Aden: A hard-won truce in the battleground Yemeni city of Hodeida will collapse if rebel violations persist and the United Nations does not intervene, the Saudi-led coalition said on Wednesday.

"A total of 21 violations since ceasefire commencement have come to our notice," a coalition source told AFP.

"If the UN continues to drag the chain and take too long to get into the (military) theatre, they will lose the opportunity altogether... and the agreement will turn a dead duck," the source said speaking in English.

Iran-backed Al Houthis were accused of violating a truce mediated by the United Nations to avert a full-scale assault on a port city vital for food and aid supplies, and pave the way for peace negotiations.

Residents reported shelling late on Tuesday, the first day of the truce, for nearly one hour on the eastern and southern outskirts of the Al Houthi-held Red Sea city, a lifeline for millions. It was calm early on Wednesday.

The United Nations is due to convene the Iran-aligned Al Houthi group and the Saudi-back government by video link on Wednesday to discuss a troop withdrawal from Hodeida city and three ports under the truce deal agreed at UN-led talks in Sweden last week, the first in more than two years.

The United Arab Emirates news agency WAM quoted a Yemeni source as saying Al Houthis fired mortar bombs and rockets at the May 22 hospital in eastern suburbs.

Hodeida, the main port used to feed Yemen’s 30 million people, has been the focus of fighting this year, raising global fears that a full-scale assault could cut off supplies to 15.9 million people.

A Saudi-led alliance, which receives arms and intelligence from the West, intervened in the war in 2015 to restore the legitimate government of Abd Rabbu Mansour Hadi that was ousted from the capital, Sana’a, in 2014 by Al Houthis, who control major population centres.

Coalition-backed Yemeni forces have massed on the outskirts of Hodeida to try to seize the port and weaken the Al Houthi group by cutting off its main supply line.

The truce, the first significant breakthrough in peace efforts in five years, was part of confidence-building steps to pave the way for a wider truce in the impoverished Arabian Peninsula country and a framework for political negotiations.

Under the deal, international monitors would be deployed in Hodeida and all armed forces would pull back completely within 21 days of the start of the ceasefire.

The UN video conference will be the first meeting of the Redeployment Coordination Committee that would oversee the ceasefire and troop withdrawal. It includes three military and security representatives from both sides.

The committee will be chaired by retired Dutch Major General Patrick Cammaert who is expected leave New York later this week to travel to Yemen with a team.

The UN Security Council is considering a resolution to ask UN chief Antonio Guterres to submit proposals by the end of the month on how to monitor the ceasefire and redeployment of forces.