The Republican party has been swift to counter the claims, with Steve Schmidt, spokesman for John McCain, the Republican presidential candidate, condemning the Democrats and the media for creating a "faux media scandal designed to destroy the first female Republican nominee''.

Al Jazeera's Rosiland Jordan in St Paul, Minnesota, says that organisers have been very quiet about what the audience will hear, but they say it will answer the questions over her experience, and also how a politician does not have to have worked much in Washington DC and in international organisations in order to be vice-president.

McCain 'grateful'

Rudy Giulani, the former mayor of New York city and presidential candidate, also said he was "confident" Palin could handle the pressure.

In focus

In-depth coverage of the US election

Giuliani is himself scheduled to speak at the convention on Wednesday evening local time.

Mitt Romney and Mike Huckabee, former governor of Massachusetts and former governor of Arkansas respectively, who also contested the Republican presidential nomination, will also speak.

Meanwhile John McCain, the Republican presidential hopeful, arrived at Wednesday in Minnesota for the convention, where he was greeted by his family and Palin along with her family.

McCain said on Tuesday that he was satisfied that Palin's background was properly checked, telling reporters in Philadelphia, Pennsylvania that "the vetting process was completely thorough and I'm grateful for the results."

'Independent man'

"We live in a dangerous world and we need a president who understands the lessons of September 11 - that man is John McCain"

George Bush, US president

Analysts said the disclosures about Palin were proving an unwelcome distraction for Republicans working to wrest the political spotlight away from the Democratic party and its candidate, Barack Obama.

Obama became the first African-American to be nominated as a presidential candidate for a major US party last week at the party's convention.

Earlier on Tuesday evening George Bush, the US president,  gave a speech remotely by satellite link - a significantly diminished role from earlier plans to take centre stage on the convention's first day.

He had been scheduled to address the convention on its first day but cancelled after Hurricane Gustav swept across the US state of Louisiana.

Bush, whose popularity levels are at record low levels, said McCain was an "independent man who thinks for himself", in a move to distance himself from the Arizona.

He praised McCain for backing his Iraq "surge" policy and said the former naval pilot who spent years in Vietnam as a prisoner of war would not have his resolve broken by "the angry left".

"We live in a dangerous world and we need a president who understands the lessons of September 11, 2001: That to protect America, we must stay on the offence, stop attacks before they happen, and not wait to be hit again," he said.

"The man we need is John McCain."

More prominent speaking roles on Tuesday went to Joe Lieberman, the Democrats' vice-presidential candidate in 2000 and now an independent senator, and Fred Thompson, the former actor and rival to McCain who dropped out of the presidential race earlier this year.