The official, who was not authorised to discuss the matter publicly, criticised Hamas officials for taking part in negotiations when only Sinwar, the leader of the terrorist group’s military wing, dictates policy.
“Ultimately Sinwar is the guy who says ‘yes’ or ‘no’,” they said.
Israeli media on Thursday evening reported that Egypt, a key mediator between Israel and Hamas, has offered a new ceasefire proposal to a visiting Israeli delegation.
Egyptian officials have suggested Israel agree to cancel the Rafah offensive and pledge a one-year ceasefire in exchange for the release of hostages, according to Yedioth Ahronoth newspaper.
An Egyptian delegation is expected in Israel on Friday to push the deal further.
Late on Wednesday, Hamas released the first proof-of-life videos for 24-year-old Hersh Goldberg-Polin who was captured in southern Israel on Oct 7. The dual Israeli-US national appeared pale and distressed.
“Sinwar made the decision he’d rather hold him and others rather than secure the ceasefire in Gaza – that’s the truth of the situation,” the US official said, adding that it appears that Mr Sinwar, one of the masterminds of the Oct 7 massacre, “seems determined to simply sit underground holding hostages, totally impervious to the conditions above ground for the people of Gaza”.