"We will continue to implement the death penalty for all those who are so sentenced," Hamas interior minister Fathi Hamad told a press conference, adding that spying for Israel was a "red line" for the Islamist-run government.
"Anyone who finds himself in this treacherous condition is an agent and a spy. He is providing information without regard to who he really is, and should be brought to justice," he said.
"If there is a death sentence we will implement it immediately in order to preserve our people and its project of jihad (holy war) and liberation."
Rights groups roundly condemned the Hamas government's pre-dawn execution by firing squad of two alleged "collaborators" last Thursday, saying there was little chance of them having been given a fair trial in the besieged territory.
Amnesty International called the executions – the first in Gaza in five years – an "extremely retrograde step by Hamas" and said the two men were convicted in "unfair military proceedings."
Hamad hit back at such groups, saying "they should speak about the crimes of the (Israeli) agents and not the justice that we are carrying out."
Last week's executions were the first to be officially carried out in Gaza since Hamas seized power in June 2007 after routing forces loyal to the Western-backed Palestinian president Mahmud Abbas.
However, the US-based Human Rights Watch has said Hamas killed at least 32 alleged informers and political opponents during and after the 2008-2009 Gaza war with Israel and maimed dozens of others.
Human rights groups say 14 people were known to have been sentenced to death by military courts in Gaza last year after being convicted on charges of "collaboration," treason and murder.
Palestinian law says the president must approve all execution orders before they can be carried out, but Hamas no longer recognizes the legitimacy of Abbas, whose four-year term ended in 2009.
Israeli security forces routinely use Palestinian informers in the occupied territories, who play a key role in thwarting attacks and in the assassinations of top militants.