The United Nations on Sunday said air raids struck Yemen's Red Sea province of Hodeida for three days, damaging a water plant and placing civilians at "extreme risk".
"On 26, 27 and 28 July, air strikes occurred near a reproductive health centre and public laboratory in Hodeida and hit and damaged a sanitation facility in Zabid and a water station, which supplies the majority of the water to Hodeida City," the office of the UN humanitarian coordinator for Yemen said in a statement.
"These air strikes are putting innocent civilians at extreme risk," the statement said.
The UN office said that "damage to sanitation, water and health facilities jeopardises everything we are trying to do" and warned "we could be one air strike away from an unstoppable epidemic".
The strikes comes less than one month after the United Arab Emirates, part of a Saudi-led coalition backing the Yemeni government, said it had suspended an offensive to take the port city to give UN mediation efforts a chance.
Speaking on condition of anonymity, Yemeni military sources contacted by AFP confirmed that air raids had resumed after the coalition said a Saudi oil tanker in the Red Sea was attacked on Wednesday.
On June 13, Saudi Arabia and its allies in a pro-government coalition launched a major offensive to retake Hodeida, through which 70 percent of Yemen's food imports flow.
The fighting around Hodeida has raised UN fears of a new humanitarian catastrophe in a country already standing at the brink of famine and gripped by a deadly cholera epidemic.
The Red Sea port has been controlled by Iran-backed Houthi rebels since 2014, when they drove the government out of the capital Sanaa and much of the country.
Earlier this year, the coalition imposed a near-total blockade on the port alleging it was being used as a conduit for arms smuggling to the rebels by its regional arch rival Iran.
The UN envoy to Yemen has reportedly been pushing for a deal to end the violence in which the rebels cede control of the port to a UN-supervised committee.
The UAE has rejected the Houthi's offer, demanding an unconditional withdrawal from the port and city.
Nearly 10,000 people have been killed in the war between Yemen's government and Houthi insurgents, including 2,200 children.