"The Israeli massacres represent a direct opening battle and that means the earthquake in the Zionist cities will resume and the herds of occupiers have no choice but to prepare the coffins or the departing luggage," Izz al-Din al-Qassam Brigades, the armed wing of Hamas, said on Friday.
Sami Abu Zuhri, a Hamas spokesman, confirmed the group would renew its attacks.
"I believe that amid the continued bloodshed of our people and the horrific images of massacres, there is no place for silence."
But Mark Regev, spokesman for the Israeli foreign ministry, said the Brigades' statement meant little because Hamas had been helping other groups to carry out rocket attacks well before Friday.
Israeli air strikes and artillery fire killed 10 Palestinians on Friday, the highest Palestinian toll in a single day since late 2004, Palestinian officials said. Around 35 people were injured.
Among the dead were three siblings aged one, three and 10, along with their parents at a beach in the northern Gaza Strip.
Two of three siblings killed in the
Palestinians said seven people in all were killed at the beach by an Israeli shell. The army said it was too early to be certain.
"This may have been an accident which caused an artillery shell to fall off course, or an older unexploded shell which went off, or perhaps an explosive device which was tinkered with," Major-General Yoav Galant, head of the southern command, said.
He said he was sorry for the loss of civilian life.
Israel said it was investigating whether its forces were responsible for the beach killing in an area it had been shelling to stop resistance fighters from firing rockets over the border.
Dan Halutz, the Israeli military's chief of general staff, later suspended the bombardments.
Israel earlier killed three men in an air strike on what the army said was a rocket crew. Palestinians said they were civilians. Rocket fire had intensified on Friday following Israel's killing of a senior militant the day before.
One of the dozens of injured
Palestinians receiving treatment
Ismail Haniya, the Palestinian prime minister, who is also a Hamas leader, called the Israeli beach attack a "war crime" and urged Jordan and Egypt, both mediators in past Israeli-Palestinian talks, to intervene.
Hamas, which has run the Palestinian government since March after winning parliamentary elections in January, spearheaded a bombing campaign during a Palestinian uprising that broke out in 2000.
UN, US reaction
A spokesman for Kofi Annan said the UN secretary-general "is deeply disturbed at the killing of civilians, including women and children ... and calls for a full investigation".
While France, Egypt and Russia condemned the attack, Sean McCormack, spokesman for the US State Department, said: "Let me just state what we have said before: That Israel has a right to defend itself.
"We also at the same time encourage Israel to ... consider the consequences of its actions."