The government of Ehud Olmert, Israel's outgoing prime minister, recently rejected Hamas' demands for 450 prisoners to be released in exchange for Shalit.

Palestinian prisoners

Nour Odeh, Al Jazeera's correspondent in Ramallah, said the conditions that the Palestinians are held in have already been criticised as "inhumane".

"Many of the prisons and detention centres they're held in have been deemed by Israeli courts as not fit for human use," Odeh reported.

"The latest actions ... admittedly to exact pressure on the Hamas movement in order to secure the release of Gilad Shalit, have been declared by human rights activists and prisoner rights activists as collective punishment, [which is] illegal under international law."

Dozens of women, hundreds of children, and a number of Palestinian legislators are among those held in Israeli detention centres - many without charge, according to the West Bank-based Palestinian Ministry for Prisoner Affairs.

The last round of Egyptian-mediated negotiations over the prisoner swap collapsed a week ago following disagreements on the list of Palestinians to be released by Israel.

Israeli officials have said they would be willing to re-negotiate a deal if Hamas changes some of the 150 prisoner names it put forward for release.

Ofer Dekel, the Israeli government's chief negotiator in the talks to free Shalit, has also reportedly met senior Hamas officials in Israeli jails up to three times in recent days.

"All of these steps [are] thought to be tools used by Israel to secure a swap, although that pressure is unlikely to yield results in the way that Israel wishes," Al Jazeera's correspondent said.