Israel launched new strikes against Hamas early on Tuesday and promised ‘increasing military force’ after talks on on further hostage releases stalled.

Israel launched a wave of airstrikes across the Gaza Strip early Tuesday, saying it was hitting Hamas targets in its heaviest assault in the territory since a ceasefire took effect in January.

At least 44 people were killed in the airstrikes, Gaza’s Health Ministry said.

Israeli Prime Minister Benjamin Netanyahu said he had ordered the strikes because of a lack of progress in ongoing talks to extend the ceasefire. It was not immediately clear if the operation was a one-time pressure tactic or if the 17-month-old war was being resumed altogether.

Hamas warned that Israel’s new airstrikes breached their ceasefire and put the fate of hostages in jeopardy.

Israeli officials said the latest operation was open-ended and was expected to expand.

“Israel will, from now on, act against Hamas with increasing military strength,” Israeli Prime Minister Benjamin Netanyahu’s office said.