"Strategically, it (the US) is setting the stage and covering up for the upcoming American war in the region," Khaled Mashaal told a press conference at a forum of Palestinian intellectuals in Damascus, where the political chief of the militant Palestinian faction has his headquarters.
Therefore, America is distracting us with a false game and is preparing itself for the real one," he said.
He spoke as US Secretary of State Condoleezza Rice met Monday in Ramallah with Palestinian President Mahmoud Abbas, Mashaal's rival, to prepare the ground for the conference.
The meeting is expected to be held later this year in the US to try to restart Palestinian-Israeli peace negotiations.
At a news conference with Rice, Abbas said he was receiving "encouraging signs" from Israel that pointed to a "real possibility" for achieving a peace deal.
Meanwhile, Mashaal said he feared "voluntary concessions by the Palestinians and the Arabs" during the upcoming conference without reciprocal moves by the Israelis.
The Hamas leader warned Arab states to stay away from the conference and advised Abbas against making any concessions.
"No one is authorized to continue with negotiations like he wishes" while the Palestinians are divided, he said. "No one is authorized to give up an inch of land, exchange it or give up the right of return."