Eleven alleged informants, all men, were killed in an open area at the Jazawat installation in Gaza City Thursday and had previously been sentenced by Gaza courts.
An additional seven executions took place outside Al-Umaria mosque in central Gaza.
Israel is often able to convince Gazans to inform on Hamas, and the militant group often metes out their punishment under circumstances like Thursday's, when they have been dealt a significant blow.
The airstrikes overnight Wednesday and into Thursday in the southern town of Rafah killed two of its most senior commanders, Mohammed Abu Shamalah and Raed Attar, both in involved in the 2006 kidnapping of Israeli soldier Gilad Shalit. The strikes also killed Mohammad Barhoum, a local commander in Rafah.
The group "was saddened over the deaths of our brothers and commanders who went on the path of great ones," said Ismail Haniyeh, the former head of Hamas in Gaza in a statement on the Hamas television network. "After a senior operative is killed, we immediately continue on our path without hesitating or stepping back."
Three of those executed Thursday were among a group of seven suspected of collaborating with Israel who were arrested while searching for targets for Israel.
Also this week a senior Hamas official living in exile in Istanbul claimed to give the group credit for the kidnapping and murder of three Israeli teens that set off the conflict earlier this summer.
Salah Arouri, one of Hamas' founders, said at a conference Wednesday that the Qassam Brigades, the group's military arm, carried out the abductions of Eyal Yifrach, 19, Gilad Shaar, 16, and Naftali Fraenkel, 16.
"It has been said that it is an Israeli conspiracy, and I say it isn't," Arouri said, in remarks captured on video at the World Association of Muslim Scholars event. "The al-Qassam's mujahedeen were the ones to carry out [the abduction] in show of support for the prisoners' hunger strike," he said, referring to Palestinians held in Israel.
Hamas had previously expressed support for the attack without taking credit outright. It is thought it may have chosen to confirm its involvement as a show of strength as the conflict turns in Israel's favor.