Israel bombarded the Gaza Strip with airstrikes Monday, as it continued its response to a surprise offensive by the Palestinian militant group Hamas that began Saturday morning. Israeli ministers have ordered a “complete siege” of the already blockaded and impoverished Gaza Strip, cutting off supplies of food, water and electricity to its roughly two million residents.

The Hamas attack, unprecedented in scale and scope, is the deadliest offensive that Israel has experienced in 50 years.

More than 900 Israelis have been killed, according to the Israel Defense Forces. The Palestinian Health Ministry said at least 687 people in Gaza and the West Bank have been killed.

More than 100 Israeli civilians, soldiers, and foreign nationals have also been taken hostage by Hamas, prompting Israeli Prime Minister Benjamin Netanyahu to declare that his country is at war. Israel says it is working to rescue the hostages and has regained control of areas outside Gaza after some 48 hours of fighting. The Israel Defense Forces said it struck more than 1,000 enemy targets in airstrikes on Gaza.

Hamas is a designated terrorist group backed by Iran and that has governed the Gaza Strip since 2007. Gaza, the small strip of land that is home to over 2 million Palestinians within roughly 140 square miles, is one of the most densely populated territories on Earth and has been kept under an Israeli land, air and sea blockade since 2007.