A military court in the Hamas-run Gaza Strip on Monday jailed a Palestinian convicted of "spying" for Israel to 15 years, judicial sources said.
In March two other men were given the same sentence for the same offence.
Under Palestinian law, those convicted of collaboration with Israel, murder and drug trafficking face the death penalty.
Execution orders must be approved by the Palestinian president before they can be carried out, but Hamas no longer recognizes the legitimacy of Mahmud Abbas whose four-year term ended in 2009.
The militant Islamist Hamas has carried out formal executions ordered by its courts and killings, sometimes public, of "collaborators" condemned by "revolutionary tribunals."
During last year's summer war with Israel in Gaza, men wearing uniforms of the armed wing of Hamas shot six alleged collaborators outside Gaza City's main mosque as worshippers left after midday prayers.
Meanwhile, an Israeli military court on Sunday sent five Palestinians back to jail who were freed in a 2011 exchange deal, according to a Palestinian NGO.
Israel claims the five violated the terms of their release, which included a commitment not to engage in terrorism and anti-Israel activity.
Among the five defendants is Nael al-Barghouthi, a Palestinian who spent 33 years behind bars in Israel, according to the Palestinian Prisoners' Society.
Also among the group is Samer Issawi who went on a hunger strike in order to pressure Israel to release him. He will be sent back to 20 years in prison. Issawi was first arrested in 2002 on terror charges and sentenced to 26 years in jail. He was released in the Shalit deal, but rearrested last June.
The military prosecutor told the court that since his release, Issawi had resumed “full terrorist activities”.
Before the deal with him was struck, Israel said it was willing to deport Issawi to any EU member country or any UN member country, but an EU spokesman said "Israel has not formally approached the EU on this subject."
"The case of re-jailing the detainees freed in the (Gilad) Shalit prisoner exchange deal and the Israeli authorities' use of legislation to carry this out is a malicious decision," the head of the NGO's legal unit Jawad Boulos said.
Hamas, for its part, said in a statement that the decision to re-imprison the Palestinians is evidence that the Israeli government acts "as a gang that doesn't heed the agreements it had signed."
Hamas said this Israel's action "represents a blow that disparages the efforts of the Egyptian mediator that sponsored the deal."
In the 2011 swap, Israel released 1,027 Palestinian prisoners in exchange for the release of Gilad Shalit, an Israeli soldier captured by Hamas and kept in Gaza for five years.
However, at least 60 of the Palestinians released in that deal were rearrested this summer amid a wide-ranging Israeli crackdown in which hundreds of West Bank Palestinians were rounded up following the abduction and murder of three Jewish teenagers.
Some 6,500 Palestinians are still imprisoned in Israel for various offenses.