(CNN)The United Nations is racing to avoid an imminent offensive on a major Yemeni port city considered a lifeline for the country's war-ravaged population.
The UN Security Council is conducting an urgent meeting over the expected assault on Yemen's Hodeidah. UN Secretary General Antonio Guterres said there are "intense negotiations" and his Yemen envoy is involved in shuttle diplomacy to stave off the attack.
Martin Griffiths, the UN's special envoy for Yemen, is shuttling between the Yemeni capital of Sanaa, the United Arab Emirates and Saudi Arabia to find "a way to avoid the military confrontation in Hodeidah," Guterres said at a briefing Monday.
Oxfam said the UK's Department for International Development (DFID) sent aid groups in Yemen warnings on Saturday evening for staff to evacuate the port city by Tuesday. It said the UAE had given the agency a notice to evacuate.
Oxfam's Yemen Country Director, Mohsin Siddiquey, said aid groups were "moving very fast" to evacuate staff in Hodeidah before the imminently expected attack has a "catastrophic impact."
"From our partners, we are receiving that there is a clear indication that families are leaving the city and there have already been shortages of fuel and other essential supplies," Siddiquey told CNN. He estimates that over a million people live in the greater Hodeidah area which is expected to be targeted in the offensive.
Griffiths previously said an attack on Hodeidah would "take peace off the table in a single stroke."
A Saudi-led coalition, which includes the UAE, has been in a virtual stalemate with the Houthis since a coalition offensive began in March of 2015. The Houthis control parts of the northern part of the country, while Yemen's coalition-backed government controls much of the south.
In another location Monday, a Saudi and Emirati-led airstrike hit a newly built cholera treatment center run by Doctors Without Borders, the humanitarian group said.
There were no casualties as the treatment center had no staff or patients at the time of the attack. The group suspended its activities in the location, which is Abs.
The center "is part of a larger compound with two hospitals and three observation areas," according to João Martins, head of the group's Yemen mission.
The strike, Martins said, "shows complete disrespect for medical facilities and patients. Whether intentional or a result of negligence, it is totally unacceptable. The compound was clearly marked as a health facility and its coordinates were shared with the" coalition.
"With only half of health facilities in Yemen fully functional, nearly 10 million people in acute need, and an anticipated outbreak of cholera, the (treatment center) had been built to save lives. (Doctors Without Borders) has temporarily frozen its activities in Abs until the safety of its staff and patients is guaranteed," Martins said.
The coalition didn't immediately respond to CNN questions.
Yemen's cholera outbreak has claimed 2,272 lives with 1,088,030 suspected cases, according to the World Health Organization.
The world's 'worst humanitarian disaster'
Last week, the UN said as many as 250,000 people could be killed in an offensive against the port city. The UN has already dubbed Yemen the world's worst humanitarian disaster.
The port city, held by Houthi rebels, serves as an entry point for 70% of foreign humanitarian aid into Yemen, according to the UN. It also provides the rebels with critical access to the Red Sea.
"Seven million people are completely reliant every month on food and other assistance from humanitarian organizations so Hodeidah is absolutely central to the preserving of life and if for any period, Hodeidah were not to operate effectively, the consequences in humanitarian terms would be catastrophic," said UN Humanitarian Chief Mark Lowcock at a press briefing Monday.
The UK and other European countries have long opposed the offensive. The emergency meeting was called by the UK, according to the Netherlands' UN Ambassador Karel J.G. van Oosterom. Oosterom described Hodeidah as a "lifeline" for aid deliveries in Yemen.
"The important thing is that (Hodeidah) is kept open and it is kept functioning because it is the major route in for these commercial supplies. As you know, Yemen needs a very large amount of commercial supplies, for meds and for food and for people just to go about their daily lives," said UK Ambassador Karen Pierce before a closed-door meeting on the imminent Hodeidah offensive.
But the United States, which previously stood against the offensive, appears to have offered tacit agreement. Officials issued a statement Monday that Yemen analyst Adam Baron described as a "yellow light" for the Yemen offensive.
"I have spoken with Emirati leaders and made clear our desire to address their security concerns while preserving the free flow of humanitarian aid and life-saving commercial imports," said US Secretary of State Mike Pompeo in a press statement Monday.
Will the Houthis withdraw?
The offensive also risks plunging the country into further violence as the coalition tries to wrest control of the strategic city from the rebels. A coalition takeover would tip the conflict in favor of Saudi Arabia and its allies.
"This offensive represents a huge escalation in the conflict ... a lot of it depends on how Hodeidah falls. If the Houthis dig in, this could be a bloody street battle comparable to Aleppo," Baron, the analyst, said.
But "there is the opportunity for a Houthi withdrawal and for the coalition to force a Houthi retreat," Baron adds.
"This is something that could be extremely high-risk and could cause a lot of humanitarian disruption ... there's a reason why you're seeing so much opposition in some quarters."