JERUSALEM (Reuters) - President George W. Bush will tell Israel's parliament on Thursday that letting Iran acquire nuclear weapons would be an "unforgivable betrayal of future generations".

"America stands with you in firmly opposing Iran's nuclear weapons ambitions," Bush will tell Israeli legislators on the second day of his visit to the Jewish state, according to an advance copy of a speech he was due to deliver later in the day.

Bush was in Israel to celebrate the Jewish state's 60th anniversary and try to shore up the faltering Israeli-Palestinian peace process.

In his speech to the Knesset, he planned to hammer home his view that democracy could prevail against extremism in the Middle East, where he has struggled to push his "freedom agenda".