Majd Tahhan's life is hanging by a thread.

As he lays on his hospital bed in critical condition, the 19-year-old young man's only wish is to see his imprisoned father before he parts with life.

In his 19 years, Majd, who is battling leukaemia - a cancer of the blood - has only spent two years and eight months in total with his father, Rajab.

His father was imprisoned in 1998, when Majd was only four months old, on charges of killing an Israeli settler.

Rajab was subsequently released in 2011 under a prisoner exchange deal for Israeli soldier Gilad Shalit who had been captured by Hamas, the Gaza-based Islamic Resistance Movement.

Less than three years later, Israeli occupation forces embarked on a campaign of mass arrests in the Palestinian territories when three Israeli settlers disappeared in the West Bank.

Hundreds of Palestinians were rounded up, and many of those who were released in the 2011 deal were rearrested and their sentences were reinstated, including Rajab's.

Despite having found out shortly after the incident who had carried out the kidnapping and killing of the three settlers, Israeli authorities kept those who were rearrested in prison.

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Rajab's life sentence was reinstated on "secret evidence", including claims he violated the conditions placed on him when he was released, according to the family.

"This is not about politics [...] It is an issue of depriving a son from his father. What is being asked of anyone with a conscience is to realise that there is a son in need of his father," a close relative of Majd and Rajab, told Al Jazeera from Jerusalem.

"We're not even asking for Rajab to be released because we know they won't release him. We just want the son to see his father - even for just 30 minutes," he said, adding they would be content with transporting Majd with an ambulance to the prison.

"Majd has bone marrow failure and he is not stable. He has no immunity - any germ or virus that enters his body can end his life at any moment."

When Majd descended into critical condition last week, the family reached out to non-governmental organisations and lawyers to pressure Israel, but they say that there have no positive indications so far.

The family said they submitted an official request to the Israeli Prison Service last week but have not received a response yet.

The father, Rajab, managed to smuggle a letter to his son out of Nafha prison in the south of the country, where he is currently languishing.

"Forgive me for not being next to you while you fight the disease ... forgive me for not sharing your pain," the letter read.

"Not the prison, nor the guards or the fences, can keep us apart."

Although Rajab was released in 2011, he was rearrested in 2014 under article 186 of the Israeli military order 1651.

Article 186 allows Israel to rearrest Palestinian prisoners who had been released in an exchange to serve the remainder of their original sentences based on "secret evidence" not accessible to the former prisoner or their lawyer.

In a 2015 report, the Jerusalem-based Addameer prisoner rights group said it found 62 cases since the 2011 exchange deal in which former prisoners were rearrested under article 186.

The use of the article in times of political tension can be classified as collective punishment - a violation of international law - according to the group.

"Article 186 is markedly incompatible with international standards and fair trial guarantees [...] the use of secret evidence to constantly arrest and detain individuals in occupied Palestine is also critically neglectful in the scope of international human rights law," Addameer said in the report, adding that the order "contravenes with the basic internationally recognized right of appearing before a court following detention".

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There are some 6,279 political prisoners in Israeli jails, according to Addameer. Some 465 of them are administrative detainees being held on "secret evidence", unaware of the accusations against them, and are not allowed to defend themselves in court. Their detention periods can be indefinitely renewed.

"The arrest of the former prisoners was obviously a political move used to put pressure on those who had kidnapped the settlers. They told us Rajab had violated the conditions of the deal - but that the evidence cannot be disclosed," the relative said.

The case has highlighted the double standards that Israel uses in dealing with Palestinian and Israeli prisoners.

In September, Elor Azaria, an Israeli soldier who was sentenced to prison after being caught on video shooting and killing a severely wounded Palestinian, was released for four days to celebrate the Jewish new year, Israeli media reported.

Despite the politics surrounding the issue of Palestinian prisoners, the family said their demands are solely humanitarian.

"Is it impossible? Is it unrealistic to ask for 30 minutes?" The relative said.

"We do not wish this feeling on anyone - not even on our enemies."