Gaza's crossings authority said Israel released around 150 detainees from the Palestinian territory on Monday, alleging that they had been mistreated in detention.

Israeli soldiers have rounded up hundreds of Palestinians during their more than six-month military offensive in Gaza, holding them without charge before releasing some in groups.

The latest detainees to be released were taken to Israel and returned via the Kerem Shalom border crossing before some were treated in a hospital in Rafah, in the south of the besieged territory, according to the Gaza crossings authority and an AFP journalist.

"Since the early hours of the morning, 150 prisoners from various parts of the Gaza Strip who were detained by the Israeli occupation have been released," the spokesman for the Gaza Crossings Authority, Hisham Adwan, told AFP.

"It is very noticeable that there is severe mistreatment of these prisoners, as a number of them were sent to Abu Yousef al-Najjar Hospital for treatment," he added.

The Israeli military did not comment on the release of these detainees but said the mistreatment of those in detention was "absolutely prohibited".

"Those who are not involved in terrorist activity are released back to the Gaza Strip," the military told AFP in a statement.

Last month, the crossings authority said 56 Palestinian detainees released from Israeli prisons "showed signs of torture" committed during their detention.

At the time, the Israeli military said detainees "are treated in accordance with international law".

The head of the United Nations agency for Palestinian refugees, Philippe Lazzarini, said last month that Gazans detained by Israeli forces were coming back "completely traumatised" and reporting "a broad range of ill treatment".

The reported abuses included threats of electrocution, being photographed naked, sleep deprivation and having dogs used to intimidate them, Lazzarini said.