A month-long cease in hostilities was broken by a new protest that turned violent at the Gaza border with Israel. Hamas has vowed to retaliate against what it called "Israeli aggression." Over 15 protesters have been injured.
Four Palestinians in the Gaza strip were killed on Friday, as protests erupted along the Israeli border. Two of those killed were said to be Hamas militants.
The health ministry in Gaza confirmed the deaths, saying that two of the Palestinians had been shot dead, while the two Hamas fighters were killed in an airstrike.
Israel's army said the airstrike was launched in retaliation for the shooting incident on the border that left two Israeli soldiers wounded.
Friday's incident represented a new escalation since a cease of hostilities had been mediated by Egypt a month ago, after a rocket that hit a house in central Israel had reignited tensions between Palestinians and Israelis.
An Israeli army spokeswoman said that some 5,200 Palestinians had taken part in Friday's day-long demonstrations. More than 50 Palestinians suffered various injuries during the protests.
Hamas pledges response
Gaza's rulers accused Israel of not honoring the deal that was brokered by Egypt, which the militants had hoped would lead to Israel scaling back the blockade imposed on Gaza in 2007.
Hamas also denounced that Israel had allegedly delayed the transfer of Qatari money for cash-strapped public institutions in the territory and that it had not helped ease its power shortage.
Israel, which seized Gaza in the 1967 Middle East War and pulled out its troops and settlers in 2005, says the blockade is necessary to stop weapons from reaching Hamas.
The militant group has fought three wars with Israel and fired thousands of rockets at it in the past decade.
Hamas pledged on Friday to respond to what it called "Israeli aggression."