Israeli foreign minister Avigdor Lieberman has said that Israel will not agree to any truce with Hamas, unless the bodies of two Israeli soldiers killed in action in Gaza are returned.

"If the terrorists from the other sides don't get it, don't understand it, they have to understand they will get in return the bodies of Mohammed Deif, [Ismail] Haniyeh and all of the Hamas leadership in the Gaza Strip," he warned.

"My colleagues and I will not accept any resolution, any framework, without the return of the soldiers' bodies."

He also said that Israel should continue its operation in Gaza if a ceasefire collapses, and "finish the story".

"Israel cannot afford a war of attrition," he said. "If the current ceasefire is heading towards collapse, we must take the initiative, even if it means a significant escalation. Finish the story in the shortest time possible."

While a 72-hour ceasefire continues to hold, and an Israeli delegation returned to Cairo to continue talks over a long-term truce, the Israeli Navy fired warning shots at a motorised fishing boat off the southern coast of Gaza.

"We are facing difficult negotiations," Hamas' leader in Cairo, Moussa Abu Marzouk, tweeted.

An Israeli official, speaking on condition of anonymity, said: "There is no progress in the negotiations."

Israeli government spokesman, Mark Regev, said this week that the Israeli military would be "ready to act to protect our people" if Hamas violated the agreement, while Hamas spokesman Sami Abu Zuhri said the talks were "the last chance" to agree on a long-term truce.

According to the United Nations, more than 1,900 Palestinians – mostly civilians – have been killed in Operation Protective Edge.

The Israeli military confirmed that 64 Israeli soldiers have been killed in the Gaza clashes, and three civilians were killed by Hamas rocket fire.