A Saudi-led coalition geared up on Tuesday for an assault on Yemen's main port, reports Agencies.
They are preparing to launch by far the biggest battle of a three-year-old war between an alliance of Arab states and the Houthi movement that controls Yemen's capital.
The United Arab Emirates, one of the main members of the Western-backed alliance, has set a Tuesday deadline for the Iran-aligned Houthis to withdraw from the port of Hodeidah under UN-led negotiations or face an assault.
It would be the first time since they joined the war on behalf of Yemen's exiled government that the foreign armies have attempted to capture such a well-defended major city.
Hodeidah, Yemen's biggest port and the only port controlled by the Houthis, serves as the lifeline for the majority of Yemen's population, which lives in Houthi-ruled territory.
The United Nations said it was engaged in "intense" shuttle diplomacy between the Houthis and coalition leaders Saudi Arabia and the UAE to avert the attack.
It estimates 600,000 people live in the area, and in a worst-case scenario a battle could cost up to 250,000 lives, as well as cutting off millions from aid and supplies.
Emirati-led troops have advanced along the southwestern coast to the outskirts of Hodeidah under a coalition strategy to box in the Houthis in the capital Sanaa and choke off their supply lines to force them to the negotiating table.
Local military sources said hundreds of Yemeni fighters as well as tanks and military supplies from the UAE arrived on Monday to reinforce troops, including Emiratis and Sudanese, in al-Durayhmi, a rural area 10 km south of Hodeidah.
Meanwhile, the United Nations (UN) is engaged in "intense" negotiations with the United Arab Emirates and Saudi Arabia in a bid to avert a military confrontation in Yemen's port city of Hudaida that could worsen.
The country's already dire humanitarian crisis, Antonio Guterres, the world governing body's chief, had said.
The UN Security Council met behind closed doors on Monday at the request of the United Kingdom to be briefed on the situation after heavy clashes were reported in Yemen's third largest city on Friday and Saturday.
"We are, at the present moment in intense consultation … I hope that it will be possible to avoid a battle for Hudaida," Guterres said.
The UN chief added that Special Envoy to Yemen Martin Griffiths was shuttling between Riyadh and Abu Dhabi.