The International Committee of the Red Cross has been given permission to fly in staff and medical supplies 12 days after a Saudi Arabia-led coalition began air strikes in Yemen.
The ICRC said this morning that it had been approved to land two planes in Sana'a, which has been hit by days of air strikes that the UN estimate have killed more than 500 people.
"We are still working on getting the plane to Sana'a. 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," ICRC spokeswoman Claire Feghali told Reuters.
But she had "high hopes" that 48 tonnes of medical supplies would be delivered by "tomorrow or the day after".
The ICRC had called for an immediate pause in hostilities to deliver life-saving medical aid over the weekend, saying three of its shipments remained blocked.
Hospitals were inundated with the wounded and were struggling to cope with medical supplies running low, it said.
Saudi Arabia imposed a no-fly zone over Yemen when it became embroiled in the conflict almost two weeks ago. Riyadh is backing forces loyal of former president Abdrabbuh Mansour Hadi, which are flight northern Houthi rebels in the southern city of Aden.
The Houthis, a northern Shi'ite tribe, took control of the Yemeni capital of Sana'a earlier this year, forcing Hadi to flee first to Aden and then to Riyadh, where he remains.
Saudi Arabia has assembled a coalition of Sunni Arab states to combat the Houthis, which it claims are backed by Iran in an effort to destabilise Riyadh's neighbour.