The stance could undercut Palestinian efforts to ease an eight-month-old Western economic boycott by forming a unity cabinet more acceptable to Israel and its closest ally, the United States.
The United States and its partners in the Quartet of Middle East mediators imposed the boycott to pressure Hamas, which took control of the Authority in March, to recognize Israel's right to exist, renounce violence and accept existing peace deals.
Hamas spokesman Fawzi Barhoum said the program of the proposed unity government between Hamas and Palestinian President Mahmoud Abbas's Fatah faction "will not recognize Israel and will not include accepting the two-state solution."
"We reject the two-state solution, which is the vision of US President George Bush, because it represents a clear recognition of Israel," Barhoum said.
"Our position in this regard remains unchanged. We reject joining in any government that recognizes Israel."
The United States and the European Union regard Hamas as a terrorist organization and have cut off direct aid to its administration. As a result, the Palestinian government has largely been unable to pay its 165,000 workers since April.
'Get ready for wider operations'
Yuval Diskin, head of Israel's Shin Bet security service, told a parliamentary committee on Tuesday that Israel should be prepared to widen its military operations in Gaza because of the growing strength of Hamas and other militant groups.
Last week 19 Palestinian civilians were killed in an Israeli artillery barrage on the Gaza town of Beit Hanoun. Israel said the barrage was caused by a technical failure.
Previous attempts to form a Palestinian unity government have stalled because Fatah and Hamas, whose charter calls for Israel's destruction, could not agree on language for a platform that satisfies both Hamas and Western powers.
Frequent flare-ups in fighting in Gaza between forces loyal to Hamas and Fatah have fueled fears of civil war.
The United States and Israel have demanded that the new government adopt a platform that meets the Quartet's conditions. The Quartet is composed of the US, the EU, Russia and the United Nations.
"We expect the new Palestinian government to recognize the three principles set by the Quartet so we can move forward in the region," Zehavit Ben Hillel, a spokeswoman for Israel's Foreign Ministry, said.
Abbas's aides say he will insist on a program that explicitly endorses interim peace deals with Israel and a two-state solution to the conflict.
Some Hamas officials have said the new government's platform might be left vague, but it is unclear whether that will satisfy Israel and the United States.
A US-educated Palestinian academic is the top candidate to replace Prime Minister Ismail Haniyeh of Hamas as part of the proposed unity government. Mohammad Shabir, 60, the former head of the Islamic University in Gaza, is considered close to Hamas but he is not a member of the group.
Top officials from the Quartet planned to meet in Cairo on Wednesday to discuss the proposed unity government and a US plan to bolster Abbas's presidential guard.