Israeli troops killed at least 20 Palestinians, most of them in the northern Gaza Strip, on Sunday in airstrikes and other attacks on targets that included a school sheltering displaced Gazans, medics and residents said.They said at least 11 of the dead were killed in three separate Israeli airstrikes on Gaza City houses. The others were killed in the towns of Beit Lahiya, Beit Hanoun and Jabalia camp.For the latest updates on the Israel-Palestine conflict, visit our dedicated page.Residents said clusters of houses were bombed and some set ablaze in the three towns. The Israeli army has been operating in the towns for over 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