Israeli troops killed 17 Palestinians on Tuesday, including a son of a top Hamas leader around Gaza a day after the two sides launched talks on the core issues of their conflict.
The deadliest single day of Israel violence in months saw the son of Hamas leader Mahmud Zahar killed.
Palestinian president Mahmud Abbas branded the Gaza operation a "massacre" and said it flew in the face of peace efforts.
"What happened today is a massacre, a slaughter against the Palestinian people," Abbas told reporters in the West Bank town of Ramallah. "Our people cannot keep silent over these massacres. These massacres cannot bring peace."
Since the two sides formally relaunched peace talks at a US-hosted conference in late November, 116 Palestinians have been killed by Israeli fire in Gaza, according to an count.
Hamas decreed three days of mourning and a general strike on Wednesday.
The Israeli assaults on Gaza have sown further discord between Israel and the Palestinians, who are also angry over the expansion of Jewish settlements on occupied land in the West Bank despite the revived negotiations.
Last Mod: 15 Ocak 2008, 18:26
Among the dead were 14 members of Hamas's armed wing, including Hossam Zahar, the son of Hamas's former foreign minister Mahmud Zahar.
The identities of the three others killed were not immediately known. About 45 other Palestinians were wounded.