The International Committee of the Red Cross said it dispatched an aircraft to Sanaa, its first aid shipment since the international campaign against Shiite rebels began last month.
"This is the first ICRC plane to have landed in Sanaa. It is loaded with 16 tonnes of medical aid," said Marie Claire Feghali, the organisation's spokeswoman in Yemen.
Residents and officials in Aden said the southern city was pounded overnight after Huthi Shiite rebels and renegade army soldiers loyal to former president Ali Abdullah Saleh arrived at the city's northern entrance.
"The raids began at around 10:00 pm (1900 GMT) on Thursday and were the most violent since the start of 'Operation Decisive Storm'," a resident told AFP.
Residents also said coalition aircraft targeted other positions, including a stadium in the centre of the city and checkpoints manned by the rebel forces.
More than two weeks of heavy bombardment by the Saudi-led alliance against opponents of exiled Yemeni President Abedrabbo Mansour Hadi and fighting between rival militias has prompted calls for urgent humanitarian intervention the impoverished nation.
The UN's children agency UNICEF said it had delivered 16 tonnes of aid by air to Sanaa on Friday.
It said the shipment contained medical supplies for 80,000 people as well as food supplements for 20,000 children.
"The supplies we have managed to bring in today can make the difference between life and death for children and their families," said UNICEF Yemen Representative Julien Harneis.
The Saudi-led coalition says it will continue its raids on Yemen until Iran-backed Huthi rebels, who seized control of Sanaa and central areas last year, retreat to their northern mountain stronghold.