Knock on the roof: how does Israel warn of airstrikes?
Israeli military hits buildings in Gaza with an unarmed 'knock on the roof' to warn of airstrikes
A YouTube video has emerged showing Israel's controversial "knock on the roof" warning system for residents of Gaza.
The video, uploaded this weekend by the Gaza-based Watania news agency, shows a warning missile fired into a house, followed by another strike minutes later that destroys the building.
What is 'knock on the roof'?
Israel fires "warning rockets" — often sent from drones — to alert residents that a buildings has been targeted, giving them time to get out before the strike comes. It is a "time-tested strategy" for the Israeli military, the Washington Post says, and is called "roof knocking".
Israel's military says that air strikes target Hamas command-and-control centres, tunnels and rocket-launching pads.
The warning rocket has no warhead, and is intended only to shake the building. It is fired between three and fifteen minutes before armed missiles hit.
Israel also phones Palestinians to alert them of impending airstrikes. In 2006, reporting the introduction of the technique, The Guardian says Gaza resident Mohammed Deeb was told: "Hi, my name is Danny. I'm an officer in Israeli military intelligence. In one hour we will blow up your house."
The military also uses radio and leaflets to warn Gazans of imminent attacks.
Do warnings work?
Amnesty International's Philip Luther has condemned the knock on the roof tactic as dangerous and ineffective. "There is no way that firing a missile at a civilian home can constitute an effective 'warning'. Amnesty International has documented cases of civilians killed or injured by such missiles in previous Israeli military operations on the Gaza Strip," Luther said.
Why warn before an attack?
Israel uses warning tactics to "avoid charges of indiscriminate killings or even of crimes against the rules of war", the New York Times says.
According to Israel's interpretation of international law, if a warning has been issued, and not heeded, the victim is no longer a 'non-combatant' but a voluntary 'human shield', Eyal Weizman says in the London Review of Books.
But some critics argue that warnings are themselves a form of psychological warfare, the Washington Post says. There are reports of "warnings" that have not been followed by airstrikes and, conversely, attacks that have come with no warning at all.
Both warning shots and phone calls demonstrate Israel's immense reach, Weizman says.
"Israel can penetrate Gaza's communication networks so easily because its telephone networks and internet infrastructure are routed through Israeli servers, which has advantages both for the gathering of intelligence and the delivery of propaganda," he says.
Human rights groups argue that whether a warning is issued or not, targeting civilians is a violation of international humanitarian law.