Antonio Guterres, the United Nations (UN) Secretary-General has called for an immediate ceasefire in Yemen and the resumption of all commercial imports to combat the growing humanitarian crisis in the country.

The warring parties to stop all ground and air assaults because “millions of children, women and men risk mass hunger, disease and death”, he said.

It comes after five days of street fighting in the capital Sanaa between the forces of Yemen's former president, Ali Abdullah Saleh, and the Iran-backed Shia rebels known as Houthis.

The two sides originally joined together three years ago and swept across Sanaa, forcing the country's internationally recognised president, Abed Rabbo Mansour Hadi, to flee the country and seek military intervention led by Saudi Arabia.

The oil rich Middle Eastern kingdom and a coalition of other powers then began a brutal aerial bombing campaign which the UN estimates to have killed more than 10,000 people and displaced more than three million.

The number of people killed in a cholera outbreak alone reached over 2,000 in September, according to Oxfam.

After months of political and military stalemate, the street battles have marked a turning point in the conflict.

The situation in Yemen Show all 14 1 /14 The situation in Yemen The situation in Yemen Houthi supporters trample on a US flag during a gathering mobilizing more fighters into several Yemeni battlefronts, in Sana'a, Yemen EPA The situation in Yemen People carry the coffins of men, who were killed in the recent Saudi-led airstrikes during their funeral, in the Old City of Sanaa, Yemen AP The situation in Yemen Pro-government fighters give food to Yemeni children on the road leading to the southwestern port city of Mokha. Yemeni rebels are putting up fierce resistance in a key Red Sea port city where they are encircled by pro-government force Getty Images The situation in Yemen A Yemeni stands in front of a graffiti protesting US military operations in war-affected Yemen, in Sana'a, Yemen. According to reports, US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen US Special Forces troops allegedly disembarked from US helicopters in the Yemeni town of Yakla and attacked several houses belonging to members of the terrorist group Al-Qaeda, killing three high-ranking Al-Qaeda members and nine civilians, six women and three children. One American serviceman has been killed and three injured in the attack EPA The situation in Yemen A Yemeni female fighter supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, takes part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen Yemeni female fighters supporting the Shiite Huthi rebels, and carrying weapons used for ceremonial purposes, take part in an anti-Saudi rally in the capital Sanaa Getty Images The situation in Yemen A boy shouts slogans next to pro-Houthi fighters, who have been injured during recent fighting, during a rally held to honour those injured or maimed while fighting in Houthi ranks in Sanaa, Yemen Reuters The situation in Yemen Balls of fire and smoke rise from a Houthi-held military camp following alleged Saudi-led airstrikes, in Sana'a, Yemen EPA The situation in Yemen Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty Images The situation in Yemen A Yemeni boy looks on as Yemenis search under the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa Getty The situation in Yemen A Yemeni boy sits amidst the rubble of damaged houses following reported Saudi-led coalition air strikes on the outskirts of the Yemeni capital Sanaa AFP/Getty The situation in Yemen Marine One with US President Donald Trump flies with a decoy and support helicopters to Dover Air Force Base in Dover, Delaware, for the dignified transfer of Navy Seal Chief Petty Officer William 'Ryan' Owens who was killed in Yemen Getty Images The situation in Yemen US President Donald Trump aboard the Marine One to greet the remains of a US military commando killed during a raid on the al Qaeda militant group in southern Yemen on Sunday, at Dover Air Force Base, Delaware, US Reuters

Clashes between fighters loyal to Mr Saleh and the Houthis first erupted last week when he accused the rebels of storming his giant mosque in Sanaa and attacking his nephew, the powerful commander of the special forces, Tarek Saleh.

Both sides have set up checkpoints, placed snipers on rooftops and sealed off entrances to the city. Bombings and sporadic gunfire rocked the southern part of Sanaa over the weekend, when Houthi militants stormed Mr Saleh's Yemen Today TV network, beat up its director, and held over 40 journalists and crew members inside the building, Yemen's Press Syndicate said.

Many state institutions — including the airport, state TV headquarters and the official news agency — remained under the control of the Houthis, despite earlier reports that Mr Saleh's forces had taken them over.

In Mehwat, a province in northern Yemen, sporadic fighting also broke out between Mr Saleh's supporters and the Houthis, while heavy fighting rocked the western district of Gidr in Sanaa province, where tribesmen took over military camps briefly before surrendering them to the Houthis.

Medical officials in Sanaa said nearly 75 people from both sides were killed and wounded in clashes there. The officials, who spoke on condition of anonymity because they were not authorised to brief media, did not provide a breakdown of the casualties.

Meanwhile, Mr Hadi, who is in Saudi Arabia in self-imposed exile, appeared to extend an offer of reconciliation to Mr Saleh.

In a statement from the country's capital Riyadh, Mr Hadi said his side would support "any party confronting Houthi terrorist gangs."