Shalit's mother Aviva called on Prime Minister Benjamin Netanyahu to do everything he could to secure freedom for her son, who was seized by Gaza-based militants in a deadly cross-border raid in June 2006.

"You have the chance of freeing Gilad," she told a gathering from a makeshift podium outside the premier's residence.

On August 3, the soldier's father Noam appealed in an open letter to Palestinians in Gaza to pressure their Hamas rulers to agree to release his son in a prisoner exchange.

Hamas and other militant groups have demanded a swap involving hundreds of Palestinian prisoners, including several top militants.

Israel made its most recent offer late last year through a German mediator, but Hamas has yet to formally respond to the deal. Each side has blamed the other for the failure to reach an agreement.

On Saturday, Aviva Shalit said she would continue a sit-in in a tent outside the Netanyahu residence, begun two months ago, and would not return home until her son was free.

Both France and Britain marked the birthday of Shalit -- who also has French citizenship -- by calling for his release.

French President Nicolas Sarkozy, in a message read out by a French diplomat, said Paris was working hard for his freedom.

"Gilad is not a prisoner of war, for PoWs have rights such as visits from humanitarian organisations or exchanges of mail with their loved ones. Gilad does not have these rights because he is a hostage," Sarkozy's message said.

He denounced "this revolting way of treating a human being which provokes our collective indignation, in Israel, France and across the globe."

Britain also used the occasion of Shalit's birthday to condemn his "unjustifiable" detention.

"The thoughts of many in Britain are with Gilad Shalit and his family as he spends his 24th birthday in captivity," a Foreign Office spokesman said in London.

"His detention is unjustifiable and unacceptable. The British government demands his immediate and unconditional release."