"The humanitarian situation is still deteriorating," Rabab al-Rifai with the International Committee of the Red Cross told the German Press Agency dpa in a phone interview from Sanaa, the Yemeni capital.
Saada governorate in the north, the main area affected by fighting between Shiite Houthi rebels and government forces, remained volatile.
A Houthi spokesman said Sunday that a Saudi airstrike had killed 54 civilians, including woman and children, though this could not be independently confirmed. Homes were also said to have been destroyed in the attacks.
Saudi Arabia, Yemen's northern neighbor, has stepped up its attacks against rebel positions, after saying militants with the Houthis crossed the border into the kingdom.
"Clearly the impact of the conflict on civilians is quite big. Lots of people are having to leave their homes, and leave everything, or almost everything behind, when they try to move and take refuge in safe areas," said al-Rafai.
"Many people, we believe, did not find it safe to move and find refuge. We believe there are lots of people still in danger," she noted.
According to rough United Nations estimates, some 150,000 people have been displaced by the fighting, with many living in or around refugee camps.
"Some conflict affected areas are unreachable. This is not only in the Saada governorate but also in Amran governorate further south of Saada," al-Rafai said.
The areas remained generally off limits even to the neutral Red Cross, owing to airstrikes and continuous attacks. The organization enters unstable zones only when it received pledges of safety from all warring parties.
The medical organization Medecins Sans Frontier (Doctors without Borders) named Yemen as one of the 10 worst humanitarian crises of 2009.
Civilians in the north were in need of food, water, shelter and medical assistance, aid workers said.
The Red Cross called on both sides to the conflict to respect international law and spare civilians the effects of the fighting. dpa sg zar mga