An Israeli air strike has killed the commander of the Hamas military wing in Gaza and Israel pounded dozens of targets in the area in the most intense attack since an Israeli offensive four years ago.
The killing of Ahmad Jabari marked a dramatic resumption of Israel's policy of assassinating Palestinian militant leaders and the Israeli military said it was the beginning of a major offensive codenamed Pillar of Defence.
Palestinians called for harsh retaliation, with thousands of angry Gazans chanting "Retaliation" and "We want you to hit Tel Aviv tonight". The air strikes came after a weekend exchange of Gaza rocket fire and Israeli air strikes appeared to have abated. The Israeli offensive is likely to reignite the conflict.
A string of air strikes around Gaza followed. The military said its aircraft targeted more than 20 facilities which served as storage or launching sites for rockets. Among the weapons destroyed were rockets that could hit as far as 25 miles (40km) into Israel.
Hamas announced a state of emergency in Gaza. It evacuated all its security buildings and deployed its troops in Gaza away from their locations.
Mr Jabari was the most senior Hamas official to be killed since the last war in Gaza ended in early 2009. He has long topped Israel's most-wanted list, blamed for in a string of deadly attacks, including the kidnapping of Israeli soldier Gilad Schalit in 2006.
In addition to Mr Jabari, nine other people were killed in the strikes. Of the nine, three were confirmed as militants, two were children and the identity of others had yet to be determined, said Gaza health official Ashraf al-Kidra. A further 30 people were injured.
Israel's prime minister said the military is prepared to broaden its operation against Hamas targets in Gaza. Benjamin Netanyahu said Israel cannot tolerate continued rocket attacks against its citizens.
Palestinian militants have responded with rocket fire. The military said its "Iron Dome" defence system has intercepted 13 rockets from Gaza. Israeli media said the rockets were shot down over the city of Beersheba.
Egypt has recalled its ambassador to Israel in response to the Israeli air strike, while the US administration of Barack Obama has given full support to the Israeli air strikes on the Gaza Strip. The UN Security Council is meeting urgently in private on Israel's military action in Gaza. The closed session on Wednesday night comes in response to a letter from Egyptian Ambassador Muutaz Khalil.