The United Nations on Friday demanded that all parties in war-torn Yemen grant civilian and commercial access to the country's ports and airports.

"Today, millions of people in Yemen are facing a triple tragedy: the specter of famine, the world's largest ever single-year cholera outbreak, and the daily deprivation and injustice of a brutal conflict that the world is allowing to drag on and on," said Stephen O'Brien, the under-secretary general for humanitarian affairs. 

"I renew my call ... to address the following points: ensure that all ports -- land, sea and air -- are open to civilian -- including commercial -- traffic," O'Brien said, adding that the airport in the capital Sanaa should be opened "immediately" to humanitarian aid.

The airport is held by the rebel Huthi fighters who also control the rest of the capital, but airspace over Yemen is dominated by the rival Saudi-led Arab coalition, which is helping the Yemeni government fight the Iran-linked Shiite rebels.

O'Brien also called on all the parties in the conflict "to respect international humanitarian and human rights law" by protecting civilians and infrastructure. 

As well as Sanaa airport, he singled out allowing the dispatch of "desperately needed mobile cranes to Hudaydah port, which handles some 70 percent of imports into Yemen and is the closest port of entry to the majority of people who need humanitarian assistance."

Britain's deputy ambassador to the United Nations, John Allen, added that "in terms of the ports or indeed the airports, we want to see any proposal that anyone can bring forward to make that humanitarian access happen."

Another diplomat said however that "no progress" had been made on a joint declaration made in June by the UN Security Council, which called on all warring parties in Yemen to facilitate aid deliveries to the country.

The diplomat, who asked not to be identified, said that political talks remained deadlocked and concerns were growing over the risk of famine, cholera and the lack of access to humanitarian aid

"Death looms for Yemenis by air, land and sea," said the UN special envoy to Yemen, Ismail Ould Cheikh Ahmed.

O'Brien also pointed to air strikes for adding to the civilian death toll. 

The Saudi-led military coalition largely controls the country's airspace, although US drones also carry out strikes on suspected Al-Qaeda bases there.

"In 2017, the number of air strikes per month is three times higher than last year, and monthly reports of armed clashes are up by more than 50 percent," he said.

He also urged member states to reach into their pockets to aid the relief effort, noting that only 39 percent of the $2.3 billion needed had so far been donated.  

More than 8,300 people have been killed and 44,000 wounded since the Saudi-led coalition entered the Yemen war in 2015. 

Close to 2,000 Yemenis have also died of cholera since April and another 600,000 are expected to contract the infection this year.