Israeli fighter jets have bombed targets in the northern Gaza Strip for the second time in three days after a Palestinian group said it carried out a rocket attack on the Israeli city of Ashkelon.
There were reports of casualties in Sunday morning's strikes, the Associated Press news agency reported without giving further details, and Israel ordered the closure until further notice of the Erez border crossing for people and the Kerem Shalom crossing for goods.
A group known as the Sheikh Omar Hadid Brigades said it fired a rocket at southern Israel on Saturday night. Israeli media reported that it struck open ground south of Ashkelon.
The southern coastal city was the apparent target of three rockets fired late on Wednesday, followed a few hours later by Israeli air strikes into Gaza.
A previous round of violence in the Gaza Strip occurred on May 26. Nobody was hurt on either side in any of the exchanges.
Local media have said the latest round of rocket fire could be related to infighting between Gaza's Hamas rulers and its opponents.
On Tuesday, Hamas security forces shot dead a Salafist leader in Gaza City during a confrontation as Hamas stepped up measures against armed groups, some of whom are known as Salafists.
Since last summer, when Israel and Hamas fought a war in and around Gaza, there have been growing signs of internal unrest between Hamas security forces and armed splinter groups.
Salafists are Sunni Muslims who promote a strict lifestyle based on that of early "pious ancestors".
In Gaza they have made no secret of their disdain for Hamas over its observance of a tacit ceasefire with Israel and what they see as Hamas' failure to implement Islamic law.