During Operation Cast Lead in Gaza in late 2008, the Israelis often used telephone calls and leaflets to tell occupants to leave before striking. In some cases, the Israelis fired missiles without explosive warheads onto the roof to get Palestinians who had gathered there to leave. The Israelis called it “the knock on the roof.” But often, as in the Khan Younis case on Tuesday, people die in any case, because they ignore or defy the warnings, or try to leave after it is too late.

And, of course, sometimes bombs and missiles do not hit the building at which they are aimed.

The Israelis also regularly drop leaflets over Gaza urging citizens not to cooperate with terrorism and to stay away from border zones, an injunction that has been criticized by human rights advocates, like the Palestinian organization Al-Haq, which argue that such leaflets do not protect Israel from allegations of the indiscriminate killing of civilians.

Groups like Human Rights Watch have regularly said that Israel’s efforts to warn civilians with phone calls and leaflets do not absolve the armed forces, which “still need to ensure that the warnings are effective and do not allow attacks otherwise prohibited under international law,” the group said in 2009, even as it welcomed “new procedures to improve its early warning to civilians during armed conflict.”

Israel also uses leaflets in Arabic, some of them intended as warnings and others as propaganda. On Tuesday, many were dropped over northern Gaza near Israel. One said that “the terrorist elements, tunnel owners and arms smugglers know very well that the continuation of the terror operations, the smuggling of arms and the digging of tunnels constitute a lasting target for the operations of the Israel Defense Forces.”