Israel has expressed regret over an Israeli artillery strike on Gaza that reportedly killed 5 people, including at least one child.
Palestinian medics told the BBC the mortar strike killed four members of one family, including two children. Other reports claimed two "youths" aged 11 and 16 were among up to five people killed.
An Israeli Defense Forces said of the deaths Tuesday: "Regrettably non-combatants were hurt, this is because Hamas attacks from civilian areas."
The latest deaths came a day after reports of as many as two dozen people being wounded in recent Israeli air strikes in Gaza. Israel has stepped up retaliatory strikes on Gaza following a barrage of rocket fire from the enclave, which is ruled by the Islamist Hamas group.
The BBC's Jon Donnison in Gaza City said the exchanges are among the most serious since Israel's major offensive between December 2008 and January 2009.
France said Tuesday it was concerned about an escalation in violence in the Gaza Strip.
"We are worried by the mounting rocket fire on Israeli territory — which we have condemned — and by the Israeli army's operations in the Gaza Strip," French Foreign Ministry spokeswoman Christine Fages told a press briefing. "We have called on both sides to show the greatest restraint in order to avoid any escalation in violence which recent history has show can have disastrous consequences."
Adham Abu Salmiya, a spokesman for Gaza emergency services, told the Ma'an news agency that members of the al-Hilu family were playing football outside their home Tuesday when the shells hit, killing Muhammad Jihad al-Hilu, 11, Yasser Ahed al-Hilu, 16, Muhammad Saber Harara, 20 and Yasser Hamer al-Hilu, 50.
An army spokeswoman said the tank shells were directed towards the location where Palestinians had fired mortars and a Qassam rocket at southern Israel earlier in the day.
Militants also fired a barrage of rockets over the frontier on Saturday, prompting Israeli retaliation. Israel launched a series of air strikes in Gaza on Monday, wounding 19 people, Reuters reported.
Adham Abu Selmeya, spokesman for Gaza emergency and ambulance services, confirmed that Israeli aircraft struck targets belonging to the armed wing of Hamas.