The Israeli operation, which started on December 27 and ended in a ceasefire on January 18, killed some 1,300 Palestinians, injured another 5,000, and caused widespread damage and destruction in the impoverished Palestinian enclave.
"The leaders of the Zionist regime killed our children in Gaza. We will demand that they be prosecuted in all international courts so that these criminals meet the punishment they deserve," Khaled Mashaal said at a meeting with students at the Tehran University.
He also said that Israel had failed to break Palestinians' resolve.
"We are preparing ourselves to liberate all of Palestine, retake Al-Quds [Jerusalem] and secure the return of all Palestinians," Mashaal said.
He also praised Iran for playing "a big role" in what he called "the victory of the people of Gaza."
Israel has long accused Iran of supplying Hamas in Gaza with weaponry, but Tehran denies these claims, saying it provides only moral support to Palestinian movements.
