Three Palestinian youths have been killed in an Israeli air strike near the border between the Gaza Strip and Israel, Palestinian officials say.
Gaza's health ministry said the dead were boys aged 13 and 14.
The Israeli military said it targeted suspected militants who approached the border fence and "were apparently involved in placing" a bomb next to it.
Hamas, the militant Islamist group which dominates Gaza, accused Israel of targeting civilians.
The incident followed another escalation over the weekend.
On Friday night militants in Gaza fired at least 30 rockets towards Israel. The Israeli military responded with air strikes on what it said were more than 80 military targets in the strip.
The militant group Islamic Jihad said it launched the rockets after Israeli troops shot dead four Palestinians during protests on Friday along the Gaza-Israel border.
The Israeli military accused Iran and Syria of giving Islamic Jihad "orders and incentives", and warned that its response was "not limited geographically".
More than 200 Palestinians have been killed by Israeli forces since the end of March - most during weekly protests along the border at which thousands have expressed their support for the declared right of Palestinian refugees to return to their ancestral homes in what is now Israel.
One Israeli soldier has been killed on the Gaza-Israel border by a Palestinian sniper during the same period.
Protesters have also demanded the lifting of the decade-long blockade of Gaza that Israel and Egypt say they impose for security reasons.
Human rights groups have accused Israeli troops of using excessive force. Israel has said they have only opened fire in self-defence or on people trying to infiltrate its territory under the cover of the protests.
Palestinians have also launched kites and balloons carrying containers of burning fuel and explosive devices over the border, sparking fires in Israel that have reportedly burned more than 2,800 hectares (6,900 acres) of forest and farmland.