The extremist movement has published a film clip where armed men line up eight people with blindfold and tied hands and then shoot them dead.
From the film clip, it appears that the execution was carried out in a square in front of a larger crowd.
"The resistance carried out the death penalty against a number of criminals and collaborators in Gaza City", it says in a statement from a Hamas-controlled TV channel.
Dozens of people were killed during the past weekend in clashes between Hamas and armed members of a powerful Palestinian clan in Gaza.
The violence is condemned by the Ramallah-based Independent Commission for Human Rights (ICHR), which in a statement demands an end to the "wave" of "extrajudicial and arbitrary executions in the Gaza Strip" since the ceasefire came into force.
