GAZA/JERUSALEM, Dec. 24 -- Israel on Tuesday carried out a series of artillery and air strikes on the Gaza Strip, killing a Palestinian girl and wounding at least five others, in response to the earlier sniper fire from Gaza that killed an Israeli worker on the separation border fence.

The strikes targeted training sites belonging to militant groups, mainly those operated by Islamic Hamas movement which controls the territory. Witnesses and security sources reported more than a dozen raids an hour after the strikes began late afternoon.

Israeli tank or artillery shells landed in front of Abu Sbaikha 's house, a mile away from the border fence in the central Gaza Strip's Al-Maghazi refugee camp, killing the four-year-old Hala and wounding two members of her family, according to Ashraf al- Qedra of the Health Ministry, adding three other people were wounded in airstrikes in Gaza City.

Israel carried out the strikes after militants from the coastal enclave shot dead an Israeli worker who were fixing the fence separating the Gaza Strip from Israel in eastern Gaza City.

"This is a very serious incident and we will not sit idly by," Israeli Prime Minister Benjamin Netanyahu said, according to a statement issued by the Prime Minister's Office. "We will respond forcefully," he added.

No Palestinian group has so far claimed responsibility for firing at the fence and killing the worker, which Israeli media reported that the worker was contracted with the Israeli Defense Ministry.

An escalation in such incidents has been witnessed across the Israel-Gaza border in the past week.

On Saturday, the Israeli soldiers fired at a group of Palestinians approaching the fence, which left one injured, saying that they aimed to sabotage the fence, whereas the Palestinians said they were just farmers who worked in their fields.

On Friday, some Palestinians approaching the fence were shot by Israeli soldiers and one of them was killed. On the same day, a group of Palestinians hurled stones at Israeli soldiers near the fence.

Since November 2012, Gaza factions and Israel have been observing a shaky cease-fire that ended an eight-day clash.

After the cease-fire, Israel canceled a buffer zone that prevented Palestinians, including farmers, from getting close to the fence and kept them away for at least 300 meters.

However, tit-for-tat shootings often take place in the border area as it remains uncertainty whether the strip is freely accessible or not.

Mahmoud Zahar, a senior Hamas official in Gaza, said Israel should not enter into the Gaza side of the fence at all. "Israel says that it can enter up to 100 meters into Gaza, and this is untrue."

Zahar condemned the Israeli strikes as "an aggression against the Palestinian people."