The International Committee of the Red Cross said on Saturday three shipments of aid and medical staff it is trying to send to Yemen were still blocked, despite appeals to the Saudi-led military coalition which controls Yemeni air space and ports.
The ICRC is seeking security guarantees for two planes to Sanaa, one with medical supplies for up to 1,000 wounded people and a second with 30 tonnes of medical and water sanitation supplies, as well as a boat to take a surgical team to Aden.
The aid organisation on Tuesday accused the Saudi-led coalition, which is waging a 10-day-old campaign of air strikes on Houthi fighters in Yemen, of preventing aid deliveries.
"Our supplies are still blocked," spokeswoman Sitara Jabeen said. "The situation is getting worse, every passing hour people are dying in Yemen and we need to bring this in urgently".
She was speaking ahead of a United Nations Security Council meeting called by Russia to discuss a humanitarian pause in the air strikes.
U.N. relief coordinator Valerie Amos said on Thursday 519 people have been killed in the fighting in the past two weeks and nearly 1,700 wounded, without specifying whether those figures included combatants.
The conflict is also taking its toll by cutting off vital services. Residents of central Aden, the southern city where Houthi fighters and their allies have been battling forces loyal to President Abd-Rabbu Mansour Hadi, said on Saturday some areas had been without water or electricity for two days.
"How can we work? This is unacceptable. How long can people live without water or electricity?" said Mohammad Fara'a, a resident of Aden's central Crater district, which was briefly captured on Thursday by Houthi forces.
Another Crater resident, Hassan Abdallah, said people were resorting to a long-disused well at one of the city's mosques to get water. In the adjacent Mualla neighbourhood, Abdu Hassan said his family was using up the last water in their tank.
"When that runs out, God knows what we will do," he said.
Uncollected rubbish was also gathering in the street, a potential health threat in the absence of running water.
Another emergency medical aid group, Medecins Sans Frontieres, has also said that airport closures and naval restrictions in Yemen have prevented it from sending in medical teams and supplies.