Israeli Prime Minister Benjamin Netanyahu told the U.S. Congress on Tuesday that while his country is prepared to make deep sacrifices to achieve peace in the Middle East, a future Palestinian state will not have the same borders as it did before the Six Day War of 1967.

Netanyahu said such an arrangement would be unworkable, leaving hundreds of thousands of Israeli citizens living outside their country.

"The vast majority of the 650,000 Israelis who live beyond the 1967 lines, reside in neighbourhoods and suburbs of Jerusalem and greater Tel Aviv," Netanyahu told Congress.

"Now these areas are densely populated, but they are geographically quite small and under any realistic peace agreement, these areas, as well as other places of critical strategic and national importance, will be incorporated into the final borders of Israel."

But Netanyahu's speech was viewed by one senior Palestinian official as "a declaration of war."

Nabil Shaath said the speech was "an escalation and unfortunately, it received a standing ovation," adding that it rejected all major Palestinian demands on issues like future borders, the competing claims of Jerusalem and the fate of refugees.

Netanyahu's remarks came days after he publicly took issue with U.S. President Barack Obama's views on how the boundaries for a future Palestinian state should be drawn.

In a recent speech, Obama suggested the map of a future Palestinian state should start with the borders that were in place before the 1967 war in which Israel captured east Jerusalem, the West Bank and the Gaza Strip.

But Obama also said the two sides could use land swaps to set new borders that would allow Israel to hold onto settlements it built after the 1967 war.

Palestinian leaders have said little about the U.S. president's recent remarks, though they are in agreement with his proposition of using the 1967 lines as the basis of the final border between Israel and a future Palestine.

Prior to Tuesday, Netanyahu rejected Obama's proposal, repeatedly saying that such borders are "indefensible."

When speaking to Congress, Netanyahu repeated that word, saying Israel would "not return to the indefensible boundaries" that existed at the onset of the Six Day War.

Netanyahu also called on Palestinian President Mahmoud Abbas to make it unequivocally clear that he will "accept a Jewish state," alongside a future Palestinian state.

By putting it on public record that Abbas accepts Israel's right to exist, he will demonstrate to his people "that they are not building a Palestinian state to continue the conflict with Israel, but to end it," Netanyahu said.

The Israeli prime minister also made reference to the recent reconciliation between Abbas' Fatah movement and Hamas, the militant group that controls Gaza.

Netanyahu said the involvement of Hamas -- a group that is considered a terrorist organization in the United States -- is an immediate roadblock to peace, because Israel will not negotiate with a government backed by "the Palestinian version of al Qaeda."

Tuesday marked the second time that Netanyahu has been invited to Washington to address Congress. His last appearance in the Capital Building was in 1996, during his first stint as prime minister of Israel.

Obama was not present when Netanyahu spoke to Congress on Tuesday.

The U.S. president is currently in Britain, ahead of his participation in a G8 summit in France later this week.

With files from The Associated Press