This is the first time he has said this to Arab leaders in a formal setting, notably while in Qatar, which has played a major role in mediating the Gaza deal.
Witkoff made the statements to families of the remaining hostages while speaking about the release of Edan Alexander.
The IDF attempted to assassinate Hamas leader Mohammed Sinwar on Tuesday in a strike on the European Hospital in Khan Yunis in Gaza.
The assassination attempt occurred as the Israeli delegation for hostage and ceasefire talks arrived in Qatar on Tuesday evening.
The incident occurred during an operation on Monday night, when police officers from the Jerusalem District noticed a vehicle entering a community near Jerusalem that raised suspicion.
"When you argue between yourselves, when you're disbanding as a society, do you know who's watching? Hamas," Witkoff told hostage families.
The MKs added that so far, operational plans have been presented for the expansion of the war in Gaza, known as Operation Gideon’s Chariots.
This was the first step in a covert diplomatic effort involving multiple governments and intermediaries, according to the officials.
In April, the IDF claimed to have killed Eslaih, a member of Hamas's Khan Yunis Brigade, in a Khan Yunis strike.
Terrorists fire two rockets from Gaza into Israel • IDF intercepts Houthi missile • IDF strikes Hezbollah terrorists in southern Lebanon