Yemen- Aid flights to Yemen are being held back by "logistical problems", as violence in the country continues.
Saudi air strikes have been targeting Houthi rebels for almost two weeks.
The International Committee of the Red Cross (ICRC) was given permission to land planes carrying staff and medical supplies, by a Saudi-led coalition on Saturday.
But the flights have been unable to depart, according to ICRC spokeswoman Claire Feghali.
The UN says more than 500 people have been killed, as the Houthis battle forces loyal to beleaguered President Abdrabbuh Mansour Hadi.
"We are still working on getting the plane to Sanaa. It's a bit difficult with the logistics because there are not that many companies or cargo planes willing to fly into a conflict zone," Ms Feghali told Reuters.
However, she insisted she had "high hopes" that 48 tonnes of medical supplies would be delivered by "tomorrow or the day after".
Desperate for help
The Red Cross is also trying to deploy a team of surgeons to the battle-torn city of Aden, but said that "authorisations from all the parties involved" were necessary before this could happen.
The ICRC spent a week negotiating with the Saudi-led coalition over deliveries of supplies.
It has called for a 24-hour ceasefire in Aden, while Russia has also urged the UN Security Council to support a "humanitarian pause" in the air strikes.
Explosions on Monday shook homes in the suburbs of Aden, one of President Hadi's last strongholds.
At least 53 people died in 24 hours of clashes between rebels and pro-government fighters, AFP reports.
Food, water and electricity shortages have also mounted, with residents pleading for help to feed their families.
Student Nisman Usman said: "We have lived three days of horrors - gunshots everywhere."
Courtesy BBC News