The charity, also known as Keren Hayesod, notified the former president on Friday morning "that the event has been called off," a Bush spokesman, David Sherzer, said Saturday.

"We regret that the speech has been canceled," Sherzer said. "President Bush was looking forward to speaking about freedom and offering reflections from his time in office."

The United Israel Appeal did not respond to an emailed request for an explanation on Saturday, the Jewish Sabbath. But the Associated Press, citing a Swiss newspaper report, said charity officials were worried protests could turn violent at the speech by the 43rd American president.

It was to be held at the Hotel Wilson, named for the 28th American president, Woodrow Wilson.

Protest organizers told participants to bring an extra shoe, prompting fears that someone might re-enact an Iraqi journalist's 2008 assault on President Bush in Baghdad. The reporter hurled his own footwear as a sign of contempt.

The New York based Center for Constitutional Rights said Saturday that European human rights groups had compiled a 2,500-page Convention Against Torture complaint against Bush, seeking to trigger it once he set foot onto Swiss soil.

CCR, a law firm led by New York civil rights lawyer Michael Ratner, has for years filed a series of mixed-result lawsuits against Bush administration policies, alleging civil liberties and human rights abuses in its detention, rendition and warrantless wiretapping policies.

It systematically sued in U.S. courts on behalf of Guantánamo captives, expanding detainee rights since the Pentagon inaugurated the prison camps opened in southeast Cuba in January 2002.

It also is a party to a complaint in Spain against former Attorney General Alberto Gonzales and five other Bush era lawyers that alleges international human-rights abuses in the U.S. treatment of war on terror captives.

That complaint has been stalled for years, and a series of U.S. diplomatic cables posted on the Internet late last year by Wikileaks showed the efforts both the Bush and Obama administrations made to derail it.

Still, a Spanish magistrate has given the United States a March 1 deadline to say whether it was pursuing its own probe of the Bush legal brain trust.

Saturday, Ratner's firm all-but claimed credit for grounding Bush.

"The message from civil society is clear," it said in a statement. "If you're a torturer, be careful in your travel plans. It's a slow process for accountability, but we keep going."

Bush's spokesman countered that the Texan, who scarcely traveled abroad before his time in the White House, has been a frequent flier in retirement.

"President Bush has made several trips outside of the United States, including to South Korea, China, Japan, Brazil, Canada, and the Middle East," Sherzer said. "He gave more than 60 speeches last year, and we expect this year to be similar."