United Nations aid chief Stephen O'Brien said on Wednesday that air strikes by Saudi-led coalition airplanes on Yemen's Red Sea port of Hodeida were unacceptable and could worsen the country's humanitarian crisis.

Hodeida, controlled by Iranian-allied Houthi forces, has become a focal point of efforts to resupply the impoverished Arab state, battered by five months of war that has killed over 4,300 people.

"These attacks are in clear contravention of international humanitarian law and are unacceptable," O'Brien said of the Tuesday attacks on the port during a briefing to the 15-member U.N. Security Council.

"I am extremely concerned that the damage to the port of Hodeida could have a severe impact on the entire country, and would deepen humanitarian needs, making more people food insecure, leaving them without access to water or medicines, which could also mean the spread of disease," he said.

The United Nations has raised Yemen to its highest level humanitarian crisis, placing it alongside emergencies in South Sudan, Syria and Iraq. It has said more than 21 million people in Yemen need help, some 80 percent of the population.

O'Brien told the U.N. Security Council that Saudi Arabia had not yet made good on an April pledge of $274 million for the world body's aid appeal for Yemen, which he said needs at least $1.6 billion and is only 18 percent funded.

"Disregard for human life by all parties continues, with attacks on residential areas and civilian infrastructure having a disproportionate impact on the lives of ordinary people inYemen," O'Brien said.

The Houthis seized Sanaa last September in what they called a revolution against a corrupt government, then took over much of the country. The Saudi-backed government fled to Riyadh and Gulf Arab states intervened to try to restore it to power.

Yemen relies on imports, but a near-total blockade led by Saudi Arabia has slowed shipments to the war-torn Arabian Peninsula country to a trickle. The Arab coalition is inspecting shipments in a bid to thwart any arms deliveries to the Houthis.

"The needs of the people are massive. This is exacerbated by impediments to commercial imports, resulting in widespread scarcity of food and fuel," O'Brien said.

"This is why airports and seaports need to remain open and be used for both commercial imports and humanitarian supplies – without restrictions," he said.