Aid workers are struggling to reach needy people uprooted by conflict in northern Yemen, the International Committee of the Red Cross (ICRC) said on Friday.

The neutral humanitarian organisation estimated that 15,500 displaced people are living in difficult conditions in camps near Saada city, and that thousands more are scattered around areas that are hard to access.

"The lack of clean water and medical care are particularly serious for the displaced, the sick, the wounded, and isolated communities," the ICRC said, warning insecurity was preventing its workers from responding to urgent humanitarian needs.

"Except in Saada city and its immediate vicinity, it remains difficult or impossible for the ICRC to operate in the conflict zones of northern Yemen," it said in a statement.

Battles between Shi'ite rebels and government forces have raged on and off since 2004 in Saada province. Hundreds of people have been killed in the conflict and thousands have fled their homes.

Sunni Muslims form a majority of Yemen's 19 million people, and most of the rest are Shi'ite Zaydis. Yemeni officials say the rebels want to restore a form of clerical rule prevalent in the country until the 1960s, while the rebels say they are defending their villages against government oppression. (Reporting by Laura MacInnis; editing by Robert Hart)