"He is a prisoner, and if Zionists lie about the dead and wounded, then the fate of this soldier is their responsibility," he said.
An Israeli military spokeswoman said Israel was investigating the claims of the capture.
Lt. Col. Francona, a military analyst for CNN, said the move would be a "game changer" because the Israelis would be looking for the soldier in the section where the capture took place.
"Overall, the Israeli strategy is not going to change. They're committed to this mission," he said. But they're "going to have to make some sort of accommodation to get this guy back."
The alleged capture comes on the deadliest day of fighting between Hamas and Israel since 2009. Eighteen Israelis and 70 Palestinians died Sunday.
The last time Hamas captured an Israeli soldier -- Galid Shalit -- a prisoner exchange agreement resulted in the release of 1,027 Palestinians for one Israeli soldier.