Al Jazeera has obtained a letter by imprisoned journalist Abdullah al-Shami, in which he talks about his deteriorating health caused by a 81-day hunger strike against his detention.

The correspondent for the Doha-based media network's Arabic news channel, who has been held without charge by Egyptian authorities since August 14, wrote that he suffered from bone aches and could "barely" stand.

The letter, which was dated on April 6, was addressed to fellow detainee Mohamed Soltan and was given to Al Jazeera by al-Shami's wife, Gehad Khaled.

Al-Shami says his family, friends and fellow prisoners had "put pressure" on him to stop his hunger strike but that he was "determined, willing and hard-headed" about his freedom.

He said he was confident that both he and Soltan would be released one day and that when that happened, they would visit the West Indies together.

In another letter, the journalist, who is being held at Tora prison in Cairo, said he would not end his hunger strike until he gained his "full freedom".

His brother Mohamed, who last met Abdullah in March, said he had lost 30kg while in detention.

Al Jazeera says it is deeply concerned about al-Shami's health.

There are three other Al Jazeera journalists being held by Egyptian authorities.

Peter Greste, Mohamed Fahmy and Baher Mohamed, who work for the network's English channel, are falsely accused of providing a platform to an outlawed group.

They have been held for more than a 100 days and on Wednesday a court adjourned their trial until April 22.

UK-based rights group Amnesty International said in a statement on Wednesday that the three journalists were "prisoners of conscience" and called for their immediate and unconditional release.

Al Jazeera strongly rejects the charges and demands the immediate release of its staff.

Source: Al Jazeera