Fierce fighting in the Gaza Strip has left at least eight Palestinians dead and five Israeli soldiers wounded.
Four Israelis were wounded in southern Gaza
Most casualties occurred when clashes broke out in the town of Beit Hanoun, where the Israeli army has been trying to end Palestinian rocket attacks.
Later, four Israeli troops were wounded in a missile attack near the southern settlement of Morag, the army said.
Israeli tanks and bulldozers have also been in action in Khan Younis in the southern Gaza Strip.
The BBC's Alan Johnston in Gaza City says this was the heaviest outbreak of fighting since the Israelis took up positions around the town.
Hamas said one of its commanders was among the dead in Beit Hanoun. Others are believed to include members of the al-Aqsa Martyrs' Brigades.
Several were injured in a strike on Gaza City on Wednesday
It is not clear how the violence broke out in the northern town - but reports from the area suggest that the Israelis encountered a small group of militants from the al-Aqsa Martyrs' Brigades.
At least two bystanders appear to have died along with the gunmen and the Israelis say one of their soldiers was seriously wounded.
The operation began about 10 days ago after two Israelis, including a boy of three, were killed in a missile attack targeting southern Israel, our correspondent says.
Islamic Jihad claimed responsibility for the attack near Morag, which it said was in response to the violence at Beit Hanoun.
On Wednesday, three Palestinians - among them a five-year-old boy - were wounded when Israeli gunships fired missiles at a car carrying Hamas operatives in Gaza City.
Israeli troops were also in action in southern Gaza overnight, moving armoured vehicles and bulldozers into the Khan Yunis refugee camp.
A military spokesman said they planned to destroy buildings from which Palestinian militants fired on Israeli forces.
The latest violence follows a meeting on Wednesday between Palestinian Prime Minister Ahmed Qurei and mediators from the US, the European Union, the United Nations and Russia.
The envoys urged the Palestinian Authority (PA) to take steps to fulfil its security obligations.
"They affirmed the need for concrete steps on the ground by the PA, not passivity, in order to revive the roadmap [peace plan] and seize the opportunity represented by Israel's Gaza withdrawal initiative," a joint statement after the talks said.
Mr Qurei called on the mediators to adopt a "clear stand" on the expansion of Israeli settlements in the Palestinian territories and the barrier Israel is building across the West Bank.