"Hamas and its (military wing) hold (Israel) and its collaborators responsible for this despicable crime,” Hamas said in a statement on Friday night, hours after gunmen shot dead Mazen Fuqaha.
Israel “knows that the blood of fighters is not spilled in vain and Hamas will know how to act," the statement added.
An Interior Ministry spokesman in the Gaza Strip said Fuqaha, 38, was killed in the enclave’s Tell al-Hama neighborhood, and that an investigation had been launched in to the incident.
Khalil al-Haya, Hamas's deputy chief in the Gaza Strip, also said only Israel would benefit from the death of Fuqaha, who was released along with over 1,000 other Palestinian inmates in a 2011 prison swap deal with Israel.
"This assassination does not serve anybody but the occupiers (Israel); it is of no interest to the other parties," Haya said.
Izzat al-Rishq, another senior Hamas official, said the assassins used silencers when they shot Fuqaha in the head.
An Israeli military spokesperson declined to comment on the shooting in the Palestinian coastal sliver.
Thousands of Palestinians are expected to attend the slain Hamas official’s funeral ceremony on Saturday.