Prime Minister Benjamin Netanyahu of Israel says the country's deadly ground offensive won't end until its soldiers destroy a vast network of Hamas tunnelsthe militants use to try to attack Jewish communities outside the Gaza Strip.
Take a look inside the vast tunnel system that has become a focus in the violent struggle between Israel and Gaza.
Miles of passageways, many stocked with weapons and reinforced against explosions from above, pass near or directly beneath Israeli schools, mosques and hospitals, threading their way under some of the most densely populated terrain on Earth.
The presence of the tunnel network has long been known to Israel, but the underground grid's scope, scale and sophistication, which has become clear over the course of the current offensive, has caught many by surprise.
Hamas had released graphic videos claiming to show deadly tunnel-generated attacks inside Israel. In one video, black-clad militants shove their weapons through a tunnel entrance, then climb out and run toward what looks like an army post inside Israel.
The Israel Defense Forces said that the tunnels "are made for kidnapping and murdering Israelis. That's why we are destroying them."
Israel says it has found "kidnap kits" consisting of handcuffs and tranquilizers in some of the tunnels.
The discovery of the elaborate tunnel system - and all the deaths resulting from tunnel-related attacks - has Israelis asking why their forces didn't stop Hamas from building the tunnels in the first place. Calls are mounting for an investigation into how authorities have handled the tunnel threat.
Israeli army continues to hunt for - and destroy - any secret tunnels said to be used by Palestinian militants for cross-border attacks. So far, the army has managed to destroy dozens of shafts leading to more than 20 tunnels.
To read more about the Israel-Gaza conflict, click here.