Israeli Prime Minister Benjamin Netanyahu warned on Tuesday 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 Gaza, according to its health ministry.

Netanyahu said in a video statement on Tuesday evening that "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 new phase intended to bring the war to an end.

The Israeli premier said in his address that "from now on, negotiations will take place only under fire," before adding: "Military pressure is essential for the release of additional hostages".

Israel has vowed to keep fighting until the return of all the hostages seized by Palestinian militants during the October 2023 attack that sparked the war.

Hamas has not responded militarily so far, and in a statement urged friendly countries to "pressure" the United States to bring to an end the strikes by its ally Israel.

The White House said Israel consulted US President Donald Trump's administration before launching the strikes, while Israel said the return to fighting was "fully coordinated" with Washington.

A State Department spokesperson said that "Hamas bears total responsibility... for the resumption of hostilities".

The United Nations and countries around the world condemned the strikes, while the families of Israeli hostages pleaded with Prime Minister Benjamin Netanyahu to halt the violence, fearing for the fate of their loved ones. (AFP)