Hamas' armed al-Qassam Brigades said in a video posted on its Telegram channel on Sunday that three hostages were killed, including a U.S. citizen, in an Israeli military operation on Saturday in which some hostages were freed.
The group did not release the names of those said to be killed, but the video showed what appeared to be three unidentifiable corpses using censor bars over their faces.
"Your captives will not be released unless our prisoners are freed," the video added.
Israel rescued four hostages held by Hamas in a hostage-freeing operation in central Gaza's al-Nuseirat on Saturday which killed 274 Palestinians.
A Hamas assertion on Saturday that some hostages were killed in the operation was dismissed shortly afterwards as a "blatant lie" by an Israeli military spokesman.
The Palestinian death toll is the worst over a 24-hour period of the Gaza war for months and including many women and children, Palestinian medics said.
