The death toll in Gaza from overnight Israeli strikes has climbed to 81, hospital officials said Wednesday.

Previously, at least 60 people, including many children, were reported killed in what is likely the most serious challenge to the tenuous ceasefire deal in Gaza since it came into force earlier this month.

The new report came as the Israeli military said the ceasefire was back in effect after it carried out heavy airstrikes across Gaza.

It said Israeli forces would continue to uphold the ceasefire agreement but would respond firmly” to any violation of the deal.

The development came after Israeli Prime Minister Benjamin Netanyahu ordered the military to conduct “powerful strikes” over Gaza, accusing Hamas of violating the fragile ceasefire.

Hamas said in response that that it would delay handing over the body of another hostage.

The Aqsa Hospital in the central city of Deir al-Balah said at least 10 bodies, among them three women and six children, reached the hospital overnight after two Israeli airstrikes there.

In southern Gaza, the Nasser Hospital in Khan Younis said it received 20 bodies after five Israeli strikes in the area, of which 13 were children and two were women.

Elsewhere in central Gaza, the Al-Awda Hospital said it received 30 bodies of which 14 were children.

Netanyahu's order to launch strikes came after an Israeli official said its forces were fired upon in southern Gaza and after Hamas handed over body parts on Monday that Israel said were the partial remains of a hostage recovered earlier in the war.