Israeli aircraft bombed sites around Gaza on Thursday, killing at least 14 Palestinians, including four children playing on a soccer field.
Israel stepped up its attacks on Hamas one day after rocket fire from the Gaza Strip killed an Israeli civilian.
A medical director in Gaza said at least 27 people — including seven children — have been killed in Israeli air strikes in the past two days. The four boys who were killed Thursday ranged in age from 8 to 14. Witnesses said they were playing soccer in a field in north Gaza.
"This is a declared war from the Israelis against the Palestinians and the Hamas movement. They started it with their aggression and attacks against the innocent civilians," Fawzi Barhoum, a Hamas spokesman in Gaza, told NPR. "They didn't even give mercy to the small children. There are kids from 5 months to 15 years old. They targeted the civilians using all their kinds of weapons and techniques."
The Israeli military says it was targeting rocket-launching squads and regrets the civilian deaths.
The rocket fire from Gaza into southern Israel continued Thursday, including several long-range rockets that hit Ashkelon, a city 12 miles north of Gaza.
Israeli government spokesman David Baker said the attack on Ashkelon would not be tolerated.
"The repeated firing of rockets at Ashkelon, a major Israeli city, ups the ante for Israel. It's a clear escalation and one which we will not tolerate," Baker told NPR. "We will not allow the continued pounding of Israeli cities and towns, and we will take whatever steps necessary to stop these attacks."
But Barhoum said the attacks on Ashkelon were necessary.
"They have to protect our land and our people. It's a reply to what the Israelis are doing — the massacres and crimes against the civilians here and to balance fear on both sides," Barhoum told NPR.
The escalating violence has overshadowed the fledgling peace talks between West Bank Palestinian leaders and Israel.