Hamas does not have 40 living hostages in Gaza who meet the conditions of a proposed exchange that could lead to a cease-fire with Israel, a senior official for the militant group told The New York Times on Wednesday.

The admission, also confirmed by The Hill, generated concerns that more hostages taken in the Oct. 7 Hamas attack may be dead than previously thought.

Israel said 133 hostages of the 240 or so originally kidnapped had not been released, and it estimates that 33 have died in captivity, according to the reports.

An Israeli official, who was also not identified, said the country relayed Hamas’ assessment to mediators, who are trying to hammer out a cease-fire negotiation already snagged by disagreements over the length of the truce and the return of displaced Palestinians, the Times added.

The framework for a possible six-week pause in fighting involves Hamas releasing 40 hostages, including all the women plus sick and older men, in a trade for hundreds of Palestinian prisoners in Israel, CNN reported. But Hamas told negotiators it did not have enough captives who qualify on those terms.

After Hamas’ surprise attack in Israel left 1,200 dead in October, Israel launched a devastating counter-offensive that has reportedly killed tens of thousands of Palestinians and spawned a humanitarian crisis.

Poor conditions in Gaza have increased pressure on President Joe Biden to rethink the country’s pipeline of military aid to the Jewish state.