They said at least 11 of the dead were killed in three separate Israeli air strikes on Gaza City houses.
The others were killed in the towns of Beit Lahiya, Beit Hanoun and Jabalia camp.
Residents said clusters of houses were bombed and some were set ablaze in the three towns.
Palestinians accuse Israel of carrying out ethnic cleansing to depopulate the northern edge of Gaza. (AP PHOTO)
The Israeli army has been operating in the towns for more than two months.
In Beit Hanoun, Israeli forces besieged families sheltering in Khalil Aweida school before storming it and ordering them to head towards Gaza City, the medics and residents said.
Medics said several people were killed and wounded during the raid on the school while the army detained many men.
The number killed was not immediately clear.
There was no immediate comment from the Israeli army.
Israel's offensive has displaced most of Gaza's population and left much of the enclave in ruins. (AP PHOTO)
Palestinians accuse Israel of carrying out ethnic cleansing to depopulate the areas at the northern edge to create a buffer zone.
Israel denies this and says the campaign targets Hamas militants and aims to prevent them from regrouping.
The war began when the Palestinian militant group Hamas stormed into Israel on October 7, 2023, killing 1200 - mostly civilians - and taking more than 250 hostages back to Gaza, according to Israeli authorities.
Israel then launched an air, sea and land offensive that has killed almost 45,000 people, mostly civilians, according to authorities in the Hamas-run Gaza Strip, displaced almost the entire population and left much of the enclave in ruins.
A bid by Egypt, Qatar and the United States to reach a truce has gained momentum in recent weeks but there has been no news of a breakthrough.
