"Guaranteeing Israel's security is more than a policy position for me. It is a personal commitment that will never waver."

Her remarks come as US and Israeli officials try to ease one of the worst ever crises between the US and its Middle East ally.

The dispute erupted when Israel announced plans for 1,600 new Jewish homes to be built in occupied East Jerusalem, which the Palestinians want as the capital of a future state.

'Difficult choices'

Clinton called the announcement, which came while Joe Biden, the US vice-president, was on a visit to Israel, an insult that damaged Obama's attempts to relaunch stalled negotiations.

The Palestinians pulled out of planned so-called proximity talks after the announcement and have demanded that all construction be stopped before they return to talks.

in depth

  Video:
  Israel pursues settlement growth
  Israelis protest settlement freeze
  Map of East Jerusalem housing plan
  Focus:
  Jerusalem's religious heart
  Settlements strain US-Israel ties
  Jewish settlements
  Riz Khan:
  The Middle East peace process
  The battle over Israeli settlements
  Inside Story:
  US and Israel poles apart
  Programmes:
  Israel: Rise of the right
  Holy Land Grab

On Monday, Clinton will stress that the US is determined to achieve broad Middle East peace but will say that all parties, including Israel, must make difficult choices.

"As Israel's friend, it is our responsibility to give
credit when it is due and to tell the truth when it is
needed," she is to say.

In her prepared remarks, Clinton also stresses that the situation between Israel and the Palestinians is "unsustainable".

"There is another path ... that leads towards security and prosperity for all the people of the region," she said.

"It will require all parties, including Israel, to make difficult but necessary choices."

Clinton has demanded that Binyamin Netanyahu, the Israeli prime minister, move to restore trust and confidence in the peace process, including a halt to projects in East Jerusalem.

Netanyahu will also address Aipac on Monday and is scheduled to meet Obama on Tuesday.

Although Netanyahu has apologised for the timing of the settlement building announcement, has had said his administration will not freeze construction in East Jerusalem.

But in a call to Clinton, he reportedly outlined some measures that his government would take to improve the impasse in talks.

US demands

The package has not been made public, but Israeli officials say part of it is an agreement to discuss all outstanding issues, such as the future of Jerusalem, borders, Jewish settlements and Palestinian refugees once the talks are restarted.

Netanyahu met George Mitchell, the US Middle East peace envoy, in Jerusalem on Sunday, as the US moved to restart the stalled peace process.

In her remarks to Aipac, Clinton said that the US will continue to demand Hamas, the Palestinian group that controls the Gaza Strip, renounce violence and recognise Israel as a valid state.

She repeated US calls for the release of Gilad Shalit, the Israeli soldier captured and still being held by Hamas.

Shortly before Clinton began her speech, a fake message was sent out in the name of Aipac to the media -and picked up by Al Jazeera - indicating that the group had called on the Israeli government to freeze new settlement projects, both in the West Bank and Jerusalem.

Aipac later confirmed that it had issued no such statement.