Ten Palestinian prisoners participating in a mass hunger strike in Israeli jails were placed under medical supervision as their conditions worsened, officials said Saturday.

The ten men are among 1,500 to 2,500 Palestinian prisoners on hunger strike to demand better conditions and an end to detention without trial.

Although Israeli officials and Palestinians give different numbers of hunger strikers, it is still one of the largest prison protests in years.

It involves a quarter to a half of all Palestinians held in Israeli jails, estimated at some 4,600 people. The reasons for their detentions range from throwing stones to killing civilians in brutal militant attacks.

Most them began refusing food 19 days ago, but a smaller core have been striking longer, from periods of time ranging from 40 to almost 70 days.

Prison spokeswoman Sivan Weizeman said the 10 were transferred to a prison clinic for medical supervision. Weizeman did not say when they were transferred or what medical treatment they are currently receiving.

Sahar Francis of Addameer, a Palestinian prisoner rights group, said the men were moved at different times last week. She said the men under medical supervision were those who had been on hunger strike the longest.

Another prisoner, Bilal Diab, was moved to a civilian hospital last week. He has refused food for 68 days so far.

The prisoners' chief demands are a halt to imprisonment without charges for periods ranging from months to years, in a system called "administrative detention."

They are also demanding an end to solitary confinement, and reinstating family visits from Gaza. They also have smaller demands, such as being allowed to take a photo with their families once a year, instead of just once during their prison term.

Israeli officials say they use administrative detention to hold Palestinians who pose an immediate threat to the country's security. They say they keep the evidence secret from lawyers and the accused, because it would expose their intelligence-gathering networks if it was released.

Solitary confinement is used to keep influential prisoners away from the rest of the population.

So far, Israeli prison authorities have responded by isolating the hunger strikers, denying them family visits and engaging with those prisoners who are not on strike.

The prisoners' conditions is one of the most emotive issues for Palestinians, many of whom have had a loved one behind bars at some point. They are seen as heroes, regardless of the reason for their detention.

Leading members of the militant Islamic group Hamas, which rules the tiny neighboring seaside territory of Gaza, have warned Israel that if any of the prisoners die while on hunger strike, they will retaliate.

This wave of strikes appears inspired by protests carried out by Palestinian prisoners Khader Adnan and Hana Shalabi earlier this year. Adnan refused food for 66 days to demand an end to his incarceration without trial, while Shalabi refused food for 43 days.

Adnan and Shalabi both belong to Islamic Jihad, a militant group vowed to Israel's violent destruction. Both were held in administrative detention; neither were ever charged with a crime.