Geneva: Air strikes by a Saudi-led coalition on the city of Saada in Yemen, where many civilians are trapped, are in breach of international law, despite calls for civilians to leave the area, the United Nations Humanitarian Coordinator for Yemen has said.

"The indiscriminate bombing of populated areas, with or without prior warning, is in contravention of international humanitarian law (IHL)," Johannes van der Klaauw said. "Issuing warnings of impeding attacks does not absolve the parties of their IHL obligations to protect civilians from harm."

An internally displaced woman sits with a child in a cave in the district of Khamir of Yemen's north-western province of Amran. Credit:Reuters

Scores of civilians were reportedly killed and thousands forced to flee their homes after the coalition, which includes Saudi Arabia and its Gulf Arab allies as well as Pakistan and Senegal and is backed by the United States, Britain and France, declared the entire governorate a military target, Mr Van der Klaauw said.

"Many civilians are effectively trapped in Saada as they are unable to access transport because of the fuel shortage. The targeting of an entire governorate will put countless civilians at risk," he added.