The talks were shelved two years ago, but the Obama administration is hoping for a breakthrough during the new rounds of negotiations set to begin September. 2.
"These negotiations are taking place by force of coercion and with an American summons," Khaled Mashaal told reporters in Damascus, Syria on Tuesday.
He said the talks are "illegitimate and do not commit our people to anything."
Israeli Prime Minister Benjamin Netanyahu will be negotiating with Palestinian President Mahmoud Abbas, who holds sway only in the West Bank, the territory squeezed between Israel and the Jordan River.
The Gaza Strip is ruled by Hamas, which refuses to recognize Israel.
Addressing the officials of Abbas' movement, he said: "Wake up. Do not allow for these adventures and sins to take place under your name."
Earlier this week, Netanyahu demanded that any future Palestinian state be demilitarized and recognize Israel as the Jewish homeland.
Obama plans to hold separate discussions with Netanyahu and Abbas on September 1 and then host a dinner for both leaders, which will also be attended by Egypt's President Hosni Mubarak and Jordan's King Abdullah II.
Mashaal called Mubarak and Abdullah not to take part, saying the negotiations could have "catastrophic results" for the region.
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