High school student Hamza Hamad spent 10 months in an Israeli jail for alleged links to the Islamic militant Hamas group, but was never charged with a crime.

The 16-year-old is one of the youngest among thousands of Palestinians who have been held in so-called administrative detention in half a century of Israeli military occupation.

The teen's case spotlights one of Israel's perhaps most contested policies, under which it can hold suspects for months or sometimes several years without charges. Israel says the policy is a key tool in preventing attacks on civilians, but rights activists say it violates due process.

Numbers of detainees have fluctuated, from a few dozen to hundreds at any given time, with spikes during violent periods. Detainee figures are up again since October 2015, when Palestinians, mostly acting on their own, began stabbing or ramming cars into Israelis in a series of deadly attacks.

Israeli officials also indicated they would expand the use of administrative detentions to deter possible attacks inspired by the extremist Islamic State group. Israel's security Cabinet approved the idea after a Palestinian, with purported sympathies for the group, rammed his truck into soldiers earlier this month, killing four.

Prime Minister Benjamin Netanyahu compared it to truck ramming attacks in Europe, which has seen some debate about administrative detentions as a means of countering a militant threat.

France and Britain used administrative detentions in conflicts in Algeria and Northern Ireland, but no longer permit it. Instead, they impose some controls on some suspects who have not been charged, including house arrest. The United States has held suspected militants without trial at its Guantanamo naval base in Cuba.

Rights activists say Israel's practice stands out because it presently uses administrative detentions as part of an open-ended military occupation. Israel captured the West Bank, Gaza Strip and east Jerusalem in 1967, but attempts have failed to negotiate the terms of a Palestinian state on occupied lands.

“These exceptional measures are still being used in a very routine way,” said Sari Bashi of the group Human Rights Watch.

“Military necessity can become greater during times of tension and escalation, but administrative detention needs to be an absolute last resort,” she said. “Israeli practice suggests that it is being abused.”

Israel says it needs a means of deterrence. It says more than 1,300 Israelis have been killed since the second Palestinian uprising began in 2000.

Administrative detention is only permitted if a trial could compromise intelligence sources, the Justice Ministry said. Judges monitor any extension of the initial term, usually six months, and detainees can appeal to the Supreme Court, the ministry said.

Lawyers say a proper defence is impossible because they and their clients can't see the state's purported evidence.

Hamad was first arrested in August 2015, at the age of 15, and held for 22 days at a Jerusalem compound where interrogators beat him and asked about weapons, said his mother, Worood.

Last February, a month after Hamad's 16th birthday, Israeli soldiers seized him again from his home in the village of Silwad. He was taken to the nearby Ofer detention center. His four-month stretch in administrative detention was renewed twice before his release in December.

In an interview earlier this month, the teen said there had been “no reason” for his detention.

He said he was held in a cell with nine other minors, most of them not administrative detainees. The tedium of watching TV and walking in the yard was only interrupted by a weekly Arabic lesson.

Hamad said he'll try to graduate this year, even though he lost two semesters in school, and was most passionate about tending to his horse, mule and two dozen chickens.

Israel's Shin Bet security service said Hamad is an activist in Hamas and has ties with senior figures in Hamas and in Tanzim, an offshoot of Hamas' rival Fatah. “His testimony raises suspicions that he acted toward advancing terror activities against Israeli targets,” the agency said.

It gave no specifics and did not mention Hamad's father, Muayyad, who is serving seven life terms for his role in the killing of seven Israeli soldiers as a member of a Hamas cell in the second uprising.

Worood Hammad, the mother of Hamza Hammad, and wife of Muayyad Hammad (Nasser Nasser/AP)

Hamad's mother, an English teacher, said she told her son and his two younger siblings to get a good education and do well in life. “From the beginning, after Muayyad was arrested, I raised my kids not to repeat this experiment,” she said.

Palestinian activists say Israel currently holds more than 700 administrative detainees, while Israel's prison service said there were 554 in December, a discrepancy apparently stemming in part from quick turnover and different counting methods.

Some cases have received special attention.

In recent years, administrative detainees launched hunger strikes, some for more than two months, with grave risks to their health, to win release. Some said open-ended detention is harder to bear than a prison term.

EU diplomats last month voiced concern about what they said is Israel's extensive use of administrative detention, singling out two hunger strikers and Mohammed Abu Sakha, a trainer at the Palestinian Circus School. The school runs an after-school program, teaching basic circus arts and other skills to 280 youths, including mentally disabled children.

The diplomats issued their statement days before Abu Sakha, 25, received a third six-month term. Abu Sakha will be released in June, at the earliest.

A cousin said the greatest challenge for Abu Sakha, a tight-wire artist, is not being able to work out in detention. “Now he is just sitting,” said the relative, Alaa Abo Alrob, 22.

The Shin Bet alleges that Abu Sakha is active in the Popular Front for the Liberation of Palestine, a faction that - like Hamas - has carried out attacks against Israelis. The agency said his activities “pose a threat” to security, but gave no specifics.

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Pnina Sharvit Baruch, a former Israeli army legal adviser, said the overall security situation helps determine who is placed in detention and that different criteria might be used at different times.

“If everything is rather calm, you would say only very serious cases would warrant administrative detention,” said Sharvit Baruch, a researcher at the Institute for National Security Studies. At times of heightened threat, “you could also detain people that are considered less dangerous,” she said.

HRW's Bashi said individual cases are difficult to assess because purported evidence is kept secret, but that patterns of arresting dissidents, journalists and rights activists suggest “we should be very skeptical.”

“And I cannot think of a single reason why a child should be placed in administrative detention,” she said.