A senior UN official expressed alarm on Friday at deadly strikes in Yemen's rebel-held port city of Hodeida, as the government said it was ready to attend UN-brokered talks in Geneva.

At least 20 people were killed and 60 wounded on 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.

Rebel-run media outlets have accused the coalition of carrying out Thursday's attacks in Hodeida.

But a coalition spokesman on Friday denied the charges, accusing the Huthis of having bombed the hospital and the fish market.

The nearest target hit by the coalition on Wednesday or Thursday was more than two kilometres (one mile) away from the two sites, the spokesman told a news conference in Riyadh.

'Everything at risk'

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.

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.”

In Geneva, the World Health Organisation (WHO) warned that Yemen is likely to be struck by another “major wave” of cholera cases, calling for a three-day truce to allow vaccinations.

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.

A government official told AFP the internationally recognised government would attend the meeting although it was “not optimistic” over the outcome, while there has yet been no response from the rebels.

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.