Israel is engaged in complex negotiations for the return of its hostages held in Gaza but also has principles to uphold that are vital for its security, Prime Minister Benjamin Netanyahu said at the start of a cabinet meeting on Sunday.

"There are things we can be flexible about, and there are things we cannot be flexible about, and we insist on them. We know very well how to differentiate between the two," he said while accusing Hamas of being "obstinate" in negotiations for a Gaza ceasefire deal.

"Hamas, up to this moment, remains obstinate. It has not even sent a representative to the talks in Doha. Therefore, the pressure should be directed at Hamas and (Yahya) Sinwar, not at the Israeli government," Netanyahu told the cabinet meeting.

Responding to warnings from Iran and Lebanon's Hezbollah, which have pledged to retaliate recent high-profile assassinations in Tehran and Beirut, Netanyahu also said Israel is "prepared for every threat, both on defense and on the attack. We are are determined to defend ourselves, and we are also determined to extract a very heavy price from any enemy that dares to attack us, from any theater."

(With input from agencies)