GAZA CITY, March 19 -- Israeli Prime Minister Benjamin Netanyahu warned yesterday that massive overnight strikes on Gaza were "only the beginning" and that future negotiations with Hamas "will take place only under fire".

The strikes, by far the largest since a truce took effect in January, killed more than 400 people across the Gaza Strip, according to the health ministry in the Hamas-run territory.

Netanyahu said in a video statement yesterday evening "Hamas has already felt the strength of our arm in the past 24 hours. And I want to promise you-and them-this is only the beginning".

Negotiations have stalled over how to proceed with a ceasefire whose first phase has expired, with Israel and Hamas disagreeing on whether to move to a n...