The United Nations warned fuel shortages threaten to halt all relief operations in Yemen "within days" as Saudi-led airstrikes and ground fighting killed 47 people in Aden, the country's second-largest city.

Gulf Arab states rejected any neutral venue for U.N.-brokered peace talks as a confidential U.N. report supported their allegations that regional rival Tehran had been arming Yemen's Huthi Shiite rebels since 2009.

Yemen was the poorest Arab country even before the rebellion against now exiled President Abedrabbo Mansour Hadi escalated last year and U.N. agencies said Thursday that millions were at risk from any halt to food distributions.

The bombing campaign launched by a Saudi-led coalition of Sunni Arab states on March 26 has virtually halted the delivery of both humanitarian aid and commercial goods, including fuel.

U.N. chief Ban Ki-moon said the lack of fuel was preventing agencies on the ground from distributing even those stocks already inside the country, most of which are in the hands of rebels who are under a U.N. arms embargo.

"Humanitarian operations will end within days unless fuel supplies are restored," Ban said.

He called for an "immediate resumption of fuel imports to avoid making the already catastrophic humanitarian situation in Yemen even worse."

The World Food Program said it was halting its food distribution in Yemen due to the severe fuel shortage.

The agency is in urgent need of more than 200,000 liters, or 45,000 gallons, of fuel to be able to continue distributing food supplies already in its warehouses, stocks that can feed 1.5 million people for one month.

The World Health Organization said that as of Monday 1,244 had been confirmed killed in fighting in Yemen since March 19.

It said that the collapse of access to health are had also fanned the spread of epidemic diseases, with 44 alerts of suspected outbreaks of diseases including measles, dengue fever and meningitis.

A hospital official in Aden on Friday said the latest Saudi-led airstrikes and ground fighting between the rebels and Hadi loyalists had killed 47 people.

They comprised eight civilians, 10 loyalists and 29 rebels and allied troops, the official said.

The southern port city has been the scene of fierce fighting for more than a month.

Residents said that overnight airstrikes targeted rebel reinforcement convoys headed to the city from the neighboring southern provinces of Abyan and Lahj.

Early last week, Riyadh announced a halt to the coalition air war but it has kept up its airstrikes every day since.

The U.N. chief renewed his call for an immediate ceasefire and said, short of that, there should be humanitarian pauses in areas affected by the fighting.

But Saudi King Salman and his son and defense minister, Prince Mohammed — newly elevated to deputy crown prince earlier this week — have staked immense political capital in the campaign to reinstate Hadi and have said repeatedly that it will go on until the rebels concede.

Gulf foreign ministers on Thursday rejected any venue for the U.N. talks except Riyadh, anathema for the rebels.

Iran has proposed holding United Nations talks on ending the war at a neutral venue, excluding all countries from the coalition.

But in a statement after talks at a Riyadh air base, the six Gulf Cooperation Council member states "affirmed their support to intensive efforts by the legitimate Yemeni government to hold a conference under the umbrella of the GCC secretariat in Riyadh."

Tehran has repeatedly denied Riyadh's charges of arming the rebels but a confidential U.N. report seen by AFP on Thursday gave support to the Saudi allegations.

The report by a panel of experts on the findings of an investigation into the 2013 seizure by Yemeni authorities of an Iranian ship, the Jihan, was presented to the Security Council's Iran sanctions committee last week.

The information collected by the experts "suggests that the Jihan case follows a pattern of arms shipments to Yemen by sea that can be traced back to at least 2009," the report said.

Saudi Arabia said its forces on Thursday killed dozens of rebels who had attempted their first retaliatory ground incursion of the five-week air war.

The Saudi defense ministry said that three of its troops had been killed but that the assault had been repulsed with the loss of dozens of rebel fighters and allied troops.