Israel has launched new air strikes on targets near Gaza City including Hamas buildings killing at least five people, four of them fighters loyal to Hamas.
Casualties from the strikes were rushed to Gaza City hospital
Six Palestinians were killed in similar strikes on Thursday.
They came as fighting between Hamas and rival Palestinian faction Fatah, which has left 40 people dead, continued for a sixth day.
Israeli officials said the raids were in response to Hamas rocket attacks on its soil.
On Sunday, the Israeli cabinet is to consider whether to escalate its response.
"In the next few days, Israel is going to make some decisions," Reuters news agency quoted Foreign Minister Tzipi Livni as saying.
Correspondents say the rocket attacks on Israel appeared to be an attempt to draw it into an internal Palestinian conflict, although the Israeli defence ministry has denied its attacks are linked to factional fighting.
Meanwhile, the United Nations' new envoy to the Middle East, Michael Williams, has warned that the situation in Gaza could deteriorate rapidly.
He told the Financial Times newspaper that it may become difficult to contain the violence.
It was unclear whether fresh elections would end the violence or provide a firm political basis for negotiation, he said.
Palestinian Authority President Mahmoud Abbas, who leads Fatah, may travel to Gaza from the West Bank on Friday to try to shore up the fourth Hamas-Fatah ceasefire in five days.
The trip, due to take place on Thursday, was called off at the last minute apparently over security concerns.
The infighting has left at least 40 people dead in the past five days.
In addition to launching air strikes, Israel made a small incursion into Gaza using tanks and infantry units.
Israeli media reports said the troops secured a ridge west of the southern Israeli town of Sderot and the northern tip of the strip.
A military spokesman said the force was on a "defensive operation".
The moves came after Hamas militants fired more rockets at Sderot.
The BBC's Katya Adler in Jerusalem says there is mounting speculation that Israel is planning a ground offensive into Gaza.
Israel withdrew from the Gaza Strip in 2005.