Beit Lahiya, Gaza Strip ? The warm, summery day in Gaza prompted Palestinian farmer Ali Ghalia to load his family up and head to the Mediterranean shore for some relaxation.

But the seaside picnic Friday turned to tragedy in a split second. An errant Israeli artillery shell exploded near the family. Ghalia and five family members, including three children, were dead.

“This was his first day at the beach this summer. He was taking his kids to play,” said his sister-in-law, Nasreen Ghalia. One of the survivors was his 7-year-old daughter, Hadeel, who remained hospitalized and unaware that she had lost her parents and two young siblings.

“Hadeel is now an orphan,” Nasreen said. The family ordered visitors not to break the news to the girl.

After the attack, the militant wing of the Islamic Hamas group called off a 16-month truce with Israel, raising the prospect of a new wave of fighting.

Hamas suspended a bloody campaign of suicide bombings, which have killed scores of Israelis, after the February 2005 cease-fire declaration and has largely stuck to the truce. The group now leads the Palestinian government.

“The earthquake in the Zionist towns will start again and the aggressors will have no choice but to prepare their coffins or their luggage,” the Hamas military wing said in a statement. “The resistance groups … will choose the proper place and time for the tough, strong and unique response.”

The Israeli artillery attack was part of a wider aerial and artillery bombardment of suspected Palestinian rocket-launching sites that killed a total of 10 people Friday.

The violence fueled tensions already high over Israel’s assassination of a top militant commander in the Hamas-led government a day earlier. Tens of thousands of people, including angry gunmen firing in the air, packed a southern Gaza soccer stadium for the funeral Friday.

Palestinian President Mahmoud Abbas condemned the attack on the beach as a ” genocidal crime,” called for international intervention and declared a three-day mourning period. His rival, Prime Minister Ismail Haniyeh of Hamas, called the attack a “war crime” and urged an end to recent fighting between Hamas and Abbas’ moderate Fatah movement.

The killings raised questions about whether Abbas would go ahead with referendum on establishing a Palestinian state alongside Israel despite pleas from Hamas to hold off.

Abbas is eager to restart stalled peace talks with Israel, and today was expected to formally announce a July 31 date for the referendum. An official close to Abbas said late Friday the president would make his announcement as planned.