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Yemen's mission to the United Nations has called for a ground intervention to push back a Houthi rebel offensive in the south of a country where conditions are deteriorating after weeks of fighting.

"We urge the international community to quickly intervene by land forces to save Yemen, especially Aden and Taiz," Khaled Alyemany, Yemen's Ambassador to the UN, said in a letter to the Security Council on Wednesday.

The letter obtained by Al Jazeera also called on the international human rights organisations to document "barbaric violations against a defenceless population".

The letter was addressed to the ambassador of Lithuania, which is holding the presidency of the Security Council for May, but was not yet released publicly. 

"Clearly this letter is reverberating through the halls of the UN," Al Jazeera's Gabriel Elizondo, who is reporting from New York, said. 

"This letter leaves nothing to doubt about what, according to the Yemeni government, needs to be done."

Civilians killed

At least 120 people have been killed in the Yemeni port city of Aden as fighting rages between Houthi fighters and local supporters of President Abd-Rabbu Mansour Hadi, rescue workers and residents said.

The dead included at least 40 Yemeni civilians who were trying to flee heavy fighting in Aden on Wednesday when the Houthi fighters fired shells at their boat, rescue workers told Reuters news agency.

The civilians were among some 50 people who were on the boat as it left the al-Tawahi district of Aden and headed towards safer areas in al-Buraiqa in the west.

Residents and local fighters said 40 other people, including a senior army officer, had been killed in fighting overnight in other parts of Aden, including an estimated 30 Houthi fighters and 10 local gunmen.

They said Arab coalition air strikes had helped the local fighters beat back a Houthi offensive on al-Tawahi, knocking out three tanks.

But Al Jazeera's Mohamed Vall, reporting from Saudi Arabia, said that as of Wednesday evening, al-Tawahi had fallen into the control of the Houthis.  

Among those killed overnight was Brigadier General Ali Nasser Hadi, the residents said. President Hadi later appointed Brigadier General Saif al-Baqri to replace him.

Earlier, the coalition carried out more than 30 air strikes in northern Yemen, a day after rockets were fired into the Saudi's border town of Najran.  

Yemen's Foreign Minister Riyadh Yaseen accused the Houthis of committing "genocide" and called on the international community to file charges against the armed group.   

The appeal for gound troops came as US Secretary of State John Kerry began a visit to Saudi Arabia likely to focus on the situation in Yemen.

Kerry has called for the lull in the fighting, while expressing his concern about the worsening humanitarian situation in Yemen.

The Arab coalition began air strikes in Yemen on March 26 against Iran-allied Houthi fighters, backed by forces loyal to former Yemeni president Ali Abdullah Saleh, who seized control of parts of the country, including the capital Sanaa.

The Houthis forced Hadi to flee the presidential palace in Sanaa in February and he is currently living in Saudi Arabia. 

Source: Al Jazeera and agencies