SANAA - A senior UN official expressed alarm Friday at deadly strikes in Yemen's rebel-held port city of Hodeida including at the entrance to the war-wracked country's largest hospital.

At least 20 people were killed and 60 wounded Thursday in an air strike at the Al-Thawra hospital and the bombardment of a fish market in Hodeida, according to medics and witnesses.

"This is shocking," said Lise Grande, the UN humanitarian coordinator for Yemen.

Hundreds of thousands of people depend on Al-Thawra, which is Yemen's largest hospital, she said.

"Hospitals are protected under international humanitarian law. Nothing can justify this loss of life."

Yemeni government forces backed by a Saudi-led coalition have been conducting an offensive to capture Hodeida from Iran-backed Huthi rebels, but announced last month they were pausing the assault to give UN mediation efforts a chance.

Strikes have picked up again around Hodeida since the Saudis last week said that two oil tankers operated by one of the kingdom's companies were attacked in the waters of the Red Sea.

Rebel-run media outlets accused the Saudi-led coalition of carrying out the attacks in Hodeida on Thursday, but there was no immediate response from the alliance headed by Riyadh.

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.

"Every day this week we have seen new cholera cases in Hodeida, and now this," Grande said.

"The impact of the strikes is appalling. Everything we are trying to do to stem the world's worst cholera epidemic is at risk."

Meritxell Relano, resident representative in Yemen for the UN Children's Fund, said the "senseless attack in Hodeida has destroyed families, hopes and dreams for a better future".

Yemen's war has killed nearly 10,000 people and triggered what the UN calls the world's largest single humanitarian crisis, with more than eight million Yemenis at risk of starvation.

UN envoy Martin Griffiths told the Security Council on Thursday that the United Nations will invite the warring sides for talks on September 6 in Geneva on a framework for peace negotiations.