New Hamas leader Ismail Haniya pledged support for hunger-striking Palestinian prisoners on Monday in his first comments since being elected as head of the movement that runs the Gaza Strip.

Haniya, who was chosen by the party as its new leader on Saturday, said the movement stood with the hundreds of prisoners on hunger strike in Israeli jails.

"This visit is a message to our heroic prisoners that your cause was and will remain a top priority," he said during a visit to a protest in support of the strikers in Gaza.

"Your freedom is a national duty and your dignity is our dignity," the 54-year-old added.

Hundreds of Palestinians in Israeli jails have been refusing food since April 17.

Palestinian officials say 1,500 political prisoners are participating in the strike, while Israeli authorities put the current figure at 860.

Daily protests across the occupied Palestinian territories, Israel and abroad have raged in solidarity with the prisoners, who are calling for better medical services, an end to solitary confinement, medical negligence, the denial of family and lawyer visits, and detentions without charge or trial.

Lawyers who have visited with the prisoners, now on their fourth week without food, told local media that the Israeli Prison Service (IPS) had increased raids and the use of solitary confinement, and banned detainees from the yard.

The strike is being led by Marwan Barghouti, a member of Fatah - Hamas' rival political faction.

On Sunday, Israeli authorities distributed video footage purporting to show Barghouti secretly eat in his cell.

Barghouti's wife and other Palestinian officials dismissed the video as fake and an attempt to break the hunger strikers.

Some 850,000 Palestinians have been incarcerated since Israel occupied their territories 50 years ago, Palestinian leaders say.

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Haniya, seen as a pragmatist within Hamas, was elected by its Shura Council on Saturday.

Unlike his predecessor Khaled Meshaal, he is expected to lead the movement from Gaza.

Hamas has run Gaza since 2007, after it pushed Fatah out following a controversial election and a near civil war.

Haniya takes charge of Hamas as it seeks to ease its international isolation while simultaneously marginalising hardliners within the movement.

Last week it unveiled a new policy document that dropped its pledge that accepted a Palestinian state along the borders set before Israel occupied East Jerusalem, the West Bank and the Gaza Strip in 1967.

Israeli Prime Minister Benjamin Netanyahu symbolically tossed the document into a bin on Sunday, calling it a "hateful document" and arguing that Hamas was trying to "fool the world".