In a major U.S. policy shift, President Barack Obama said that Israel must accept its pre-1967 borders as a starting point in discussion aimed at reviving a stalled peace plan with the Palestinians.

But on the eve of a crucial summit with his Israeli counterpart, Obama's speech was met with negative reaction from many quarters, and there was concern that the president had overplayed his hand even before talks began.

During his speech Thursday, Obama said a Palestinian state should be created according to borders that existed before the Six Day War, and he stressed that Israel could never have peace if it maintained "permanent occupation" in the region.

Israeli Prime Minister Benjamin Netanyahu -- due in Washington on Friday -- quickly rejected Obama's speech as "indefensible." And reaction elsewhere was mixed, even among Obama's supporters.

Foreign policy expert James Robbins, a former special assistant in the Office of the Secretary of Defense, said Obama took "a big risk" by coming out so strongly on the border issue.

In fact, since Israel has long maintained that the pre-1967 borders are unacceptable, Obama may have already spent his political capital in advance of the meeting.

"I don't think that stating a specific endpoint like that is going to help kickoff a negotiation. He should have been more vague about it," Robbins told Â鶹ӰÊÓ Channel in an interview from Washington on Thursday.

"There's a sense among some that he's already poisoned the well," Robbins added.

During his speech Thursday, Obama implored both Israel and the Palestinians to accept two key planks aimed at reviving the moribund Middle East peace process: security for Israel and national borders for Palestine.

While Obama's words jolted Israel and upset some pro-Israel supporters in his own party, he also admonished the Palestinian leadership for attempting to gain statehood recognition through a UN vote and said that a new alliance between Hamas and Fatah was unacceptable.

"At a time when the people of the Middle East and North Africa are casting off the burdens of the past, the drive for a lasting peace that ends the conflict and resolves all claims is more urgent than ever," Obama said in his speech, which was delivered to a diplomatic audience at the State Department.

Still, the president nuanced his border proposal by saying that any agreement would allow both sides to undertake possible land swaps.

More importantly, Obama's blunt speech seems to signal a change in tactics for the White House, which has long attempted to bring Israel and the Palestinians to the table.

While the president took a harder line on Israel's presence in East Jerusalem, the West Bank and Gaza, his statement may have been designed to force Netanyahu into action and break a stalemate that has dragged on, even as other neighbouring nations in the region undergo historic changes.

"The international community is tired of an endless process that never produces an outcome," he said.

In essence, by stating that the 1967 borders are the starting point rather than a desired outcome, Obama also appeared to redraw the very complexion of any permanent deal.

"There must be no doubt that the United States of America welcomes change that advances self-determination and opportunity," the president said. "Yes, there will be perils that accompany this moment of promise. But after decades of accepting the world as it is in the region, we have a chance to pursue the world as it should be."

In the Israeli media, the reaction to Obama's contention was fast and negative.

Danny Danon, a top member of Netanyahu's Likud party, accused Obama of attempting to destroy Israel by taking a line supported by former Palestinian leader Yasser Arafat, Israeli media reported.

"Netanyahu only has one option: to tell Obama to forget about it," Danon said, according to reports.

But Obama also said that any Palestinian state should be "non-militarized" and that it would be unwise for leaders to continue a campaign to be recognized by a vote in the UN General Assembly in September.

He also said that any Palestinian alliance with Hamas -- which does not accept Israel's right to exist -- seemed to underscore concerns from Israel.

"How can one negotiate with a party that has shown itself unwilling to recognize your right to exist," he said. "In the weeks and months to come, Palestinian leaders will have to provide a credible answer to that question."

That contention was dismissed outright by some Palestinian leaders, including Hamas sources.

"The peoples of the region are not in need of Obama's lectures," said Hamas spokesperson Sami Abu Zuhri. "Obama reaffirmed his absolute support for the policies of the (Israeli) occupation and his rejection of any criticism of the Occupation."

With a report from The Associated Press