Residents in an 11-storey building were called 10 minutes before an Israeli attack on the district in Gaza and told to evacuate, after which at least two missiles slammed into the complex, levelling it totally, emergency services and witnesses said.

An Israeli army spokeswoman told AFP a Hamas military operations room had been located in the building.

Earlier on Saturday, the Israeli military sent text messages and voice mails and dropped leaflets warning Palestinians that "every house from which militant activity is carried out, will be targeted".

Israel said it had carried out 55 air strikes over the Gaza Strip on Saturday and that around 45 rockets and mortar rounds hit Israel, with another 10 intercepted as a six-week war with Hamas rumbles on.