Israel deployed ground troops inside Gaza for the first time to raid a rocket launching site in the Palestinian territory.
Ignoring international appeals for a ceasefire, Israel widened its range of Gaza bombing targets to civilian institutions with suspected Hamas ties.
More than 156 Palestinians have been killed in five days of bombardment.
Four Israeli soldiers were today hurt in clashes during the brief incursion to destroy a rocket launching site in northern Gaza, the military said. It said they have returned to Israeli territory.
It was the first time that Israeli ground troops are known to have entered Gaza in the current offensive.
But the operation was carried out by special forces and did not appear to be the beginning of a broad ground offensive.
Yesterday, Israel announced it would hit northern Gaza “with great force” to prevent rocket attacks from there on Israel.
One of the Israeli strikes hit a centre for the disabled where Palestinians said two patients were killed and four people seriously hurt.
In a second attack, yesterday evening, an Israeli warplane flattened the home of Gaza’s police chief and damaged a nearby mosque as evening prayers ended, killing at least 18 people, officials said.
In New York, the UN Security Council called unanimously for a ceasefire, while Britain’s foreign minister said he will discuss ceasefire efforts with his American, French and German counterparts today.
So far, neither Israel nor Gaza’s Hamas rulers have signalled willingness to stop.
Israel has carried out more than 1,200 air strikes this week to try to diminish Hamas’ ability to fire rockets at Israel.
The chief military spokesman, Brigadier General Motti Almoz, said there would be more strikes, especially in northern Gaza near the Israeli border.
“We are going to attack there with great force in the next 24 hours due to a very large concentration of Hamas efforts in that area,” he said.
The military said it was ordering Palestinians in northern Gaza to evacuate “for their own safety”.
Gaza’s interior ministry urged residents in the area to ignore Israel’s warnings and to stay in their homes, saying the announcement was Israeli “psychological warfare” and an attempt to create confusion.
Shortly after the Israeli announcement, an Israeli warplane struck the home of the Gaza police chief, Taysir al-Batsh, killing at least 18 people and wounding 50, said health ministry official Ashraf al-Kidra.
He said worshippers were leaving the mosque after evening prayers at the time of the strike and that some people are believed to be trapped under the rubble.
Meanwhile, Hamas, the Islamic militant group that controls Gaza, has fired nearly 700 rockets and mortars at Israel this week and said it would not be the first to cease fire.
In a sign that the conflict might widen, Israel fired into Lebanon late yesterday in response to two rockets fired from there at northern Israel.
There were no injuries or damage, but Israel fears militant groups in Lebanon may try to open a second front.
Israel has said it is acting in self-defence against rockets that have disrupted life across much of the country. It also accuses Hamas of using Gaza’s civilians as human shields by firing rockets from there.
Critics said Israel’s heavy bombardment of one of the most densely populated territories in the world is itself the main factor putting civilians at risk.
Sarit Michaeli of the Israeli human rights group B’Tselem said that while using human shields violates international humanitarian law, “this does not give Israel the excuse to violate international humanitarian law as well”.
The “Iron Dome,” a US-funded, Israel-developed rocket defence system, has intercepted more than 130 incoming rockets, preventing any Israeli fatalities so far. A handful of Israelis have been wounded by rockets that slipped through.
Yesterday, air raid sirens went off in Jerusalem and Tel Aviv, Israel’s two largest cities, both located nearly 50 miles from Gaza.
Most of the rockets were intercepted or fell in open areas, though one landed near the Palestinian city of Hebron in the West Bank. A house was damaged but there were no injuries.
The frequent rocket fire has disrupted daily life in Israel, particularly in southern communities that have absorbed the brunt of it.
Israelis mostly have stayed close to home. Television channels air non-stop coverage of the violence and radio broadcasts are interrupted live with every air raid siren warning of incoming rockets.
The frequent airstrikes have turned bustling Gaza City into a virtual ghost town during the normally festive month-long Ramadan holiday, emptying streets, closing shops and keeping hundreds of thousands of people close to home where they feel safest from the bombs.
The offensive marks the heaviest fighting since a similar eight-day campaign in November 2012 to stop Gaza rocket fire.
The outbreak of violence follows the kidnappings and killings of three Israeli teenagers in the West Bank, and the kidnapping and killing of a Palestinian teenager in an apparent revenge attack.
Israel has massed thousands of troops along the border in preparation for a possible ground invasion, with soldiers atop vehicles mobilised and ready to move if the order arrives.
At the United Nations, a Security Council statement approved by all 15 members calls for de-escalation of the violence, restoration of calm, and a resumption of direct negotiations between Israelis and Palestinians aimed at achieving a comprehensive peace agreement based on a two-state solution.
The statement calls for “the reinstitution of the November 2012 ceasefire,” which was brokered by Egypt, but gives no time frame for when it should take effect.
The statement, which is not legally binding but reflects international opinion, is the first response by the UN’s most powerful body, which has been deeply divided on the Israeli-Palestinian conflict.
In London, foreign minister William Hague of Britain, a close Israeli ally, said he had spoken to his Israeli counterpart and called for an “immediate de-escalation” and expressed his “deep concern” about civilian casualties.
The Arab League said foreign ministers from member states will hold an emergency meeting in Cairo tomorrow.
Later Israel called on residents of the northern Gaza Strip to evacuate their homes, suggesting an imminent attack after its troops earlier launched a brief raid.
The Israeli air force dropped leaflets this morning calling for the evacuation. Israel’s military spokesman says troops will begin a “short and temporary” campaign against northern Gaza.
The call comes after Israeli troops launched a brief raid early today into northern Gaza to destroy what it described as a rocket-launching site. The military said four soldiers were slightly wounded in the operation.