The British Jewish community has joined international efforts to highlight Gilad Shalit's continued captivity as the soldier marks his sixth birthday since he was kidnapped by Hamas.

Sergeant Shalit, who was 19 when he was captured in Israel by Hamas terrorists while he was guarding the border with Gaza, turns 25 on Sunday.

The Board of Deputies of British Jews used the anniversary to reiterate the demand for his "immediate and unconditional release" and to urge the Red Cross to increase its efforts to gain access to him.

The Board also highlighted the facts that Sergeant Shalit had consistently been denied contact with his family, visits from the Red Cross and independent medical care.

"His treatment well demonstrates the criminal and barbarous nature of Hamas and their callous disregard for the rules of normal human decency and international law," the Board said in a statement.

"We demand that the British government, along with its EU counterparts and the international community, apply substantial pressure to Hamas to end Gilad's plight to ensure that this birthday will be the last one which he spends in captivity."

The Board recently launched the "Faces for Gilad" awareness campaign and has written to other religious organisations appealing for support.

On Facebook, a group started by British Jew Elliot Jebreel to mark Sergeant Shalit's birthday has attracted nearly 1,000 supporters.

On the group, Mr Jebreel posted campaign information and wrote: "For the sake of his family, let's do all we can to bring him home".

In Israel, Sergeant Shalit's parents wrote an open letter to their son on his birthday. Noam and Aviva Shalit wrote: "'We know that every day that passes is another nightmarish day of impossible suffering, days and nights of suffocating endless loneliness.

"But we do not forget you."

Next Tuesday, the soldier will be named an honorary citizen of Pittsburgh, in a move to raise awareness and encourage solidarity.

Sergeant Shalit has now been missing for more than five years and 60 days.