"We are at war," Israeli Prime Minister Benjamin Netanyahu said in a televised address on Saturday as Hamas, a Palestinian armed movement, carried out a surprise attack from its Gaza base.

At least 100 Israelis have been killed and 900 injured in the Hamas attack, Israeli media reported. Israel's Minister of National Security, Itamar Ben-Gvir, declared a state of national emergency throughout the country.

Over 2,500 rockets were fired into Israel by Hamas since the early hours of Saturday, said the Israeli military. It added that, in response, airstrikes against over 20 Hamas targets have been carried out in recent hours. 

The Israeli military said in a statement that the Palestinian movement "will bear the results and responsibility for the events."

Mohammed al-Deif, a leader from Hamas, announced on Saturday the beginning of a new military operation, "Al-Aqsa Flood," against Israel via a brief recorded statement.

Hamas said the attack was driven by Israel's escalated attacks on Palestinians in the West Bank and Jerusalem, as well as those against Palestinians in Israeli prisons.

The Israeli army announced that it had targeted 17 sites and four headquarters of the Hamas with dozens of warplanes in various areas of the coastal enclave.  

At least 198 people were killed and over 1,600 others were wounded in Gaza on Saturday, the Health Ministry in the Palestinian enclave said, after Israel's air strikes.

Palestinian President Mahmoud Abbas said on Saturday that the Palestinian people have the right to defend themselves against "Israeli violations."

During an emergency leadership meeting held in Ramallah, Abbas instructed the concerned Palestinian authorities to provide everything necessary "to strengthen the steadfastness of the Palestinians in the face of crimes committed by the Israeli occupation and settler gangs," Palestinian official news agency WAFA reported. 

(With input from agencies)