Israeli Prime Minister Benjamin Netanyahu told residents of Gaza City on Monday to evacuate, as the military ramped up its deadly assault on the Palestinian territory's largest urban centre.

Israel has been intensifying its bombardment of the city in preparation for an operation to conquer it, despite repeated entreaties from Western nations and aid agencies to stop.

Gaza's civil defence agency meanwhile said at least 39 people had been killed by Israel, including 25 in Gaza City, on Monday.

The premier's warning came hours after one of the deadliest attacks on civilians in Jerusalem since the start of the war, in which two Palestinian gunmen opened fire on a bus, killing six people, according to Foreign Minister Gideon Saar.

The two gunmen were killed by a security officer and an armed civilian, police said.

Following the attack, Netanyahu said: "Let it be clear: these murders strengthen our determination to fight terrorism."

Israel's defence minister, Israel Katz, had told Hamas earlier on Monday to lay down its arms or face annihilation.

"This is a final warning to the Hamas murderers and rapists in Gaza and in luxury hotels abroad: Release the hostages........

© Al Monitor