Israel said its military had carried out several strikes on the Gaza Strip
A three-year-old Palestinian girl has been killed in a series of retaliatory Israeli strikes on the Gaza Strip.
The attacks came hours after an Israeli civilian was shot dead by a Palestinian sniper while repairing the border security fence.
Israel's military said its aircraft and tanks had carried out strikes on several "terror sites", including a weapons manufacturing base.
Hamas, which governs the Gaza Strip, said it was a "dangerous escalation".
Hamas official Mushir al-Masri said on al-Aqsa television that Israel would "pay the price for these crimes" and he said Hamas and other Palestinian organisations were considering an "appropriate response".
According to reports, the girl died when Israeli shells hit the east of Maghazi refugee camp in the central Gaza Strip.
The girl's mother and two of her brothers were wounded in the attack, reports say.
A Gaza health ministry official said a man was killed in an Israeli attack in northern Gaza - but the BBC has been unable to confirm this.
The Israeli man was shot in the chest while working on the border fence near Nahal Oz. He later died in hospital.
An Israeli man was shot while working on the border fence near Nahal Oz
It was the first killing of an Israeli on the border with Gaza for since 2012.
Israeli Prime Minister Benjamin Netanyahu said the "very severe incident" would not go unanswered.
"Our policy until now has been to act beforehand and to respond in force, and this is how we will act regarding this incident as well."
The Israel Defence Forces (IDF) said the security fence was "paramount in protecting" Israeli civilians.
"The IDF will continue to operate against those who use Gaza as a safe haven for terrorism against our civilians," said Lt Col Peter Lerner.
He said Hamas was accountable for all attacks originating from Gaza.
There has been intermittent violence along the border since a ceasefire ended an eight-day conflict between Israel and militants in Gaza in November 2012.
Israel considers Gaza a "hostile territory" after it was taken over by the anti-Israel Islamist Hamas movement in 2007.