The United Nations on Monday urged Israel and Hamas to ensure humane treatment for all people they hold, saying recent images of emaciated individuals being released was "deeply distressing".
"Images of emaciated Israeli hostages and Palestinian detainees released as part of the first phase of the Gaza ceasefire agreement have been deeply distressing," UN Human Rights office spokesman Thameen Al-Kheetan said in a statement.
"The images we have seen of Israeli hostages released over the weekend show signs of ill-treatment and severe malnourishment, reflecting very dire conditions they were subjected to in Gaza," he said.
"We are also deeply concerned by the public parading of hostages released by Hamas in Gaza, including statements apparently made under duress during release," he added.
Also distressing, Al-Kheetan said, was that "Palestinians released from Israeli detention have revealed such treatment, reflecting the severe conditions under which they have been held".
"The manner in which they have been released also raises serious concerns," he added.
"Israel and Hamas must ensure humane treatment, including freedom from any form of torture or abuse, for all those held under their power."
Under the terms of the ceasefire deal between Hamas and Israel, the first phase of which came into effect on January 19, 33 Israeli hostages were to be released in exchange for around 1,900 prisoners, most of them Palestinian, being held in Israeli jails.
On Saturday they completed their fifth hostage-prisoner exchange, with three Israeli hostages and 183 Palestinian prisoners released.
Israeli Prime Minister Benjamin Netanyahu denounced Hamas as "monsters" after the handover of the three captives, who appeared emaciated and were forced to speak on a stage flanked by Hamas gunmen.
The hospital treating former hostages Or Levy and Eli Sharabi said they were in a "poor medical condition", while Ohad Ben Ami was in a "severe nutritional state".
With their return, 73 out of 251 hostages taken during the attack now remain in Gaza, including 34 the Israeli military says are dead.
Of the prisoners freed from Israeli jails, the Palestinian Prisoners' Club advocacy group said seven required hospitalisation, decrying "brutality" and mistreatment in jail.
Kheetan reminded all parties to the conflict that torture and other forms of ill-treatment of protected persons were war crimes, and that those found guilty should receive sentences that are commensurate to the severity of their conduct.
"We reiterate that the taking of hostages is a war crime," he said.
"Hamas must immediately and unconditionally release all hostages, and Israel must immediately and unconditionally release all those arbitrarily detained."