In recent days, Israeli troops have surrounded Gaza City and battled Hamas fighters as they pushed deeper into its streets.
Israeli Defense Minister Yoav Gallant approved on Monday further operational plans for military action in Gaza City and the northern Gaza Strip.
The Israeli military has said that many of Hamas' tunnels, command centres and rocket launchers lie adjacent to schools, hospitals and humanitarian institutions in northern Gaza, including the Al-Shifa hospital in Gaza City, the region's largest.
Hamas is estimated to have a force of between 20,000 and 30,000 fighters, according to Israeli security sources.
Security sources said some intelligence was being gathered from Gaza residents fleeing south about the concentration of the tunnels.
Persons:
Jonathan Saul JERUSALEM, Yoav Gallant, Daniel Hagari, Avi Melamed, Benny Gantz, Hagari, Israel, Ayman Nofal, Yaron Finkelman, Finkelman, Lior Akerman, Shin, Shalom Ben Hanan, Ben Hanan, Nidal al, Daniel Flynn
Organizations:
Israeli, Israel Defense Forces, Islamic, Southern Command, Institute for Policy, Israel's Reichman University, Shin Bet, Shin
Locations:
Gaza, Gaza City, Israel, Hamas, Washington