The International Committee of the Red Cross on Tuesday appealed for "bold measures" to provide life-saving care to civilians in Yemen after an "unprecedented" escalation of fighting in recent days.
More than 230 people have been killed and at least 400 wounded in nearly a week of fighting in the Yemeni capital, now under the control of Huthi rebels.
"Over the past days Sanaa, the capital, has witnessed the fiercest fighting since the beginning of the conflict in March 2015," the ICRC's regional head of operations, Robert Mardini, told AFP.
Heavy bombardment on Sanaa kept civilians trapped inside their homes and hit an ICRC warehouse storing medical supplies to be delivered to three of the city's strapped hospitals.
The ICRC was subsequently unable to deliver surgical kits to facilities struggling to deal with a "massive influx" of war-wounded.
"You can imagine hospitals of Sanaa that are lacking fuel to run generators and lacking medicine are in dire need of our support," Mardini said.
"It shows that the suffering of the Yemeni people has unfortunately no end in sight."
The United Nations has listed Yemen as the world's number one humanitarian crisis, with seven million people on the brink of famine and a cholera outbreak that has caused more than 2,000 deaths.
The country's health system has collapsed, and the UN on Tuesday urged a "humanitarian pause" in the fighting to allow aid to reach desperate civilians.
- Yemen 'drip-fed' for years -
But Mardini said Yemen needed more than just a temporary fix.
"This country has been drip-fed now for two years. It needs intensive care. It's not just about a couple of ships in Hodeida or a couple trucks crossing from Saudi Arabia," he said.
"Statistics always hide the tragedy of individual stories, but today there is no single Yemeni who has not suffered this conflict. The time has come now to stop this, to take bold measures."
The Saudi kingdom imposed a blockade on Yemen's ports after a Huthi missile was intercepted near Riyadh airport on November 4.
The blockade has been eased only partially, despite repeated calls from the UN.
"Unfortunately, humanitarian aid is being politicised and used as a bargaining chip, which is of course unacceptable, illegal, and immoral," Mardini told AFP.
On Monday, Huthi rebels killed former Yemeni president Ali Abdullah Saleh as he fled the capital following the collapse their uneasy alliance.
After his death, Saudi-led warplanes pounded the capital as the rebels moved to consolidate their control over the city Tuesday.
The heavy bombardment had terrified civilians in Sanaa, according to Mardini.
"Close to our office, there have been every day since the beginning of the conflict, children playing and cheering.
"That was the first time (ICRC staff) didn't hear anything," he said, adding his colleagues had not slept in five days.
"There was a deafening silence between the mortar shells. That was a very eerie sense of how war can break habits and normal life."