Israeli Prime Minister Benjamin Netanyahu's office says his Security Cabinet has declared the country at war following a deadly Hamas assault in southern Israel.

The decision, announced on Sunday, formally authorises “the taking of significant military steps,” it said it a statement.

“The war that was forced on the State of Israel in a murderous terrorist assault from the Gaza Strip began at 06:00 yesterday,” it said.

It gave no further details. But Netanyahu had previous declared the country at war, and the military has promised a harsh response in Gaza.

Israeli media say at least 600 people have been killed in the surprise cross-border incursion by Hamas militants from the Gaza Strip.