Israeli Prime Minister Benjamin Netanyahu said on Tuesday he has ordered the army to immediately carry out “powerful strikes” in Gaza, a new test for the tenuous US-brokered ceasefire.

The order from Netanyahu follows heightened tensions, as Israel reported Hamas firing on its forces in southern Gaza and after Hamas returned a set of remains that Israel said belonged to a hostage recovered earlier in the war.

Netanyahu called the return a “clear violation” of the ceasefire agreement, which requires Hamas to return all Israeli hostage remains as soon as possible.

In a sign of the fragility of the ceasefire, Israeli troops were shot at in the southern city of Rafah on Tuesday and returned fire, according to an Israeli military official who spoke on condition of anonymity because there had not been an official announcement yet.

There are still 13 bodies of hostages in Gaza. Hamas said on Tuesday it has recovered the body of a hostage that it plans to hand over this evening.

An Associated Press videographer in Khan Younis witnessed what appeared to be a white body bag being carried out from a tunnel by several men, including some masked militants, and then transported into an ambulance. It was not immediately clear what was in the bag.