In comments published in the Palestinian al-Hayat al-Jadida newspaper on Friday, Khalid Mishaal said: "We will never recognise the legitimacy of the Zionist state that was established on our land."
Mishaal heads the political and military wings of the Islamist group Hamas, which won last week's Palestinian parliamentary election by a landslide and appears set to form the next Palestinian government.
Hamas, which spearheaded a bombing campaign that has killed hundreds of Israelis over the past decade, has long said it might heed a truce with Israel as an interim measure but would not abandon its long-term goal of destroying Israel.
But in his newspaper column, titled "To whom it may concern", Mishaal said Hamas might be willing to negotiate with Israel on the conditions for such a truce.
"If you [Israel] are willing to accept the principle of a long-term truce, then we will be ready to negotiate with you over the conditions of such a truce," Mishaal said.
The United States and the European Union have called on Hamas to disarm, revoke its charter calling for Israel's destruction and halt attacks against Israel. The calls have been backed up with threats to cut aid to the Palestinian Authority.
In his column, Mishaal rejected these calls. "Our message to the United States and Europe is that the attempts you are exerting to make us abandon our principles and struggle will be wasted and will not achieve any results," he said.
Israeli officials dismissed Mishaal's suggestion of a truce as "verbal gymnastics". They said Hamas must unequivocally recognise Israel's right to exist as a sovereign state, abandon "terrorism" and destroy its "terror" infrastructure.
Mark Regev, a foreign ministry spokesman, said: "Anything short of that will simply maintain the current situation in which the absolute majority of the community of nations determine Hamas to be a terrorist organisation, and as such, not a legitimate interlocutor for political negotiation."
Ismail Haniyeh, a senior Hamas leader in the Gaza Strip, said Hamas's conditions for a long-term truce included an Israeli withdrawal from the West Bank as well as its release of all Palestinian prisoners.
Hosni Mubarak, the Egyptian president, was quoted by Israel's Yedioth Ahronoth newspaper as saying: "If Hamas wants to set up a government, then Hamas must recognise Israel."