Al-Zahar told reporters that the activists of the intifada, or rebellion against Israeli occupation, and the militants of various Palestinian factions had "forced Israel to choose the withdrawal."
Al-Zahar also said that Israel was leaving the Gaza Strip and part of the West Bank because of the armed struggle and not because of negotiations or good intentions on the part of Israel, the United States or Europe.
Israel intends to evacuate all 21 Jewish settlements in Gaza and four of 120 settlements in the West Bank starting in July under a unilateral disengagement plan.
Al-Zahar refused to commit Hamas to the peace process, saying the group was waiting to see the outcome of Israel's withdrawal from the occupied territories.
Israel and the Palestinian Authority agreed in February to end the violence that lasted four and a half years and killed 3,350 Palestinians and 970 Israelis.