At least 900 people have died and more than 2,500 others have been injured in Israel after the militant group Hamas launched an unprecedented incursion from air, land and sea on Saturday,  according to Palestinian and Israeli sources.

Hamas fired thousands of rockets toward Israel and an estimated 1,000 fighters crossed into the country from the neighboring Gaza Strip. Israeli officials said at least 100 civilians and soldiers have been taken hostage.

The Israel Defense Forces has since declared "a state of alert for war" and launched retaliatory airstrikes on Gaza, a 140-square-mile territory where 2 million Palestinians have lived under a blockade imposed by neighboring Israel and Egypt since Hamas seized power in 2007. Palestinian authorities said at least 560 people have died and another 2,900 have been injured in Gaza since Saturday. Unlike Israel, the Gaza Strip has no air raid sirens or bomb shelters.