“We have the Israelis right where we want them,” Mr Sinwar said in one of dozens of messages to ceasefire negotiators obtained by The Wall Street Journal.
The messages display a calculated disregard for human life and a belief on the part of Mr Sinwar that Israel has more to lose from the eight-month war than Hamas.
More than 37,000 people, mainly civilians, have been killed in Gaza since the start of the war, according to Hamas-controlled health authorities. The number of combatants killed remains unknown.
The messages revealed by The Wall Street Journal appear to support the view that Mr Sinwar is willing to put his political objectives above the preservation of human lives.
In one message to Hamas leaders in Doha, he cites civilian losses in national-liberation conflicts in places such as Algeria, where hundreds of thousands of people died fighting for independence from France, saying, “these are necessary sacrifices”.
In a separate letter, sent on April 11 to Ismail Haniyeh, a Hamas political leader, whose three sons were killed in an Israeli air strike, Mr Sinwar claimed their deaths and those of other Palestinians would “infuse life into the veins of this nation, prompting it to rise to its glory and honour”.