Israeli Prime Minister Benjamin Netanyahu on Sunday warned of a "long and difficult" war, as fighting with Hamas left hundreds dead on both sides after a surprise attack on Israel by the Palestinian militant group.

The conflict's bloodiest escalation in decades saw Hamas carry out a massive rocket barrage and ground, air and sea offensive Saturday that Israel's army said had killed more than 200 Israelis and wounded 1,000, while soldiers and civilians were taken hostage.

Gaza officials said intense Israeli air strikes on the coastal enclave had brought the Palestinian death toll to at least 256, with nearly 1,788 wounded.

As fighting raged Sunday, Lebanon's powerful Iran-backed Hezbollah movement said it had fired "large numbers of artillery shells and guided missiles" at Israeli positions in a contested border areas "in solidarity" with Hamas.

Israel's army had earlier said it fired artillery on southern Lebanon in response to a shot from the area without identifying the attackers.

"We are embarking on a long and difficult war that was forced on us by a murderous Hamas attack," Netanyahu said on X, formerly Twitter, early Sunday.

"The first stage is ending at this time by the destruction of the vast majority of the enemy forces that infiltrated our territory," he added, pledging no "respite" until victory.

Overnight Israel battered the Gaza Strip with air strikes as rockets from the blockaded Palestinians territory rained on Israel.

Sunday morning gun still battles raged between Israeli forces and hundreds of Hamas fighters in multiple locations, including at the Sderot police station across the border from Gaza.

Police and Israeli army special forces "neutralized 10 armed terrorists" who were holed up inside the station, a police statement said.

The bloody air, sea and land attack launched Saturday by Hamas came half a century after the outbreak of the 1973 Arab-Israeli war, taking Israel and the world by surprise.