The International Committee of the Red Cross (ICRC) called for the removal of obstacles to aid delivery and for humanitarian workers be allowed to work safely in Yemen, as Arab warplanes pounded the country for a sixth day.
It said Yemeni Red Crescent volunteer Omar Ali Hassam had been shot dead on Monday in the southern province of Al Dhalea while evacuating wounded people.
The ICRC said it had a plane stocked with medical supplies to treat up to 1,000 people that had been due to arrive in the country Tuesday but efforts to negotiate its safe arrival had so far failed.
The supplies were "for distribution to hospitals across the country that are running low on the means to treat the war wounded" after a week of deadly clashes and air strikes.
"There are casualties across the country," said Cedric Schweizer, who heads an ICRC team of 300 people in Yemen.
"There have been air strikes in the north, west and south, and clashes between opposing Yemeni armed groups in the centre and south, that are putting immense strain on already weak medical services," Schweizer said.
"In order that the wounded get the treatment they deserve, it's essential we deliver urgent medicines and surgical kits," he added.
An ICRC surgical team was due to arrive shortly in the southern city of Aden, which has suffered the biggest casualties so far, the organization said.
A Saudi-led Arab coalition has been conducting air strikes against Huthi rebels in Yemen since Thursday.
It has vowed to keep up the raids until the Iran-backed rebels abandon their insurrection against President Abedrabbo Mansour Hadi, who has fled to Riyadh.
ICRC's statement came a day after an air strike killed dozens of people and injured some 200 at a camp for displaced people in northwest Yemen, according to aid workers.