A former White House security expert has accused President Bush of doing a "terrible job" of tackling terrorism.
Aides have rejected the criticism of President Bush
Richard Clarke said Mr Bush ignored warnings of the threat from al-Qaeda before the 11 September 2001 attacks.
US officials denied this, saying the administration had developed an anti-terror strategy before the attacks.
The criticisms came as former US President Jimmy Carter accused the US and UK of going to war in Iraq based on "lies or misinterpretations".
In an interview with a British newspaper, he said that Mr Bush's commitment to finish the war against Iraq started by President George Bush senior in 1991 had prevailed over the "better judgement" of UK Prime Minister Tony Blair.
"There was no reason for us to become involved in Iraq recently," Mr Carter told the Independent.
"I think that President Bush and Prime Minister Blair probably knew that many of the allegations were based on uncertain intelligence... a decision was made to go to war [then people said] 'Let's find a reason to do so'."
Correspondents say it is very rare for a former US president to criticise an incumbent or a British prime minister.
'Ignored for months'
Mr Clarke's comments came ahead of the publication of his book, Against All Enemies, on Monday.
He said the US president had later tried to show links between al-Qaeda and Iraq, despite being told none existed.
He said it was "outrageous" Mr Bush was running for re-election on his record fighting terrorism, when in fact he had "ignored it" before the attacks.
"He ignored terrorism for months, when maybe we could have done something to stop 9/11. Maybe. We'll never know."
He said Mr Bush appeared obsessed with the idea of blaming former Iraqi leader Saddam Hussein.
"See if Saddam did this. See if he's linked in any way," Mr Clarke quotes Mr Bush as saying in the book.
"The entire conversation left me in absolutely no doubt that George Bush wanted me to come back with a report that said Iraq did this," he added.
He also told the US broadcaster CBS that the day after the 11 September attacks, Secretary of Defence Donald Rumsfeld called for retaliatory strikes on Iraq, even though al-Qaeda was based in Afghanistan.
"Rumsfeld said there aren't any good targets in Afghanistan," he said. "And there are lots of good targets in Iraq. I said: 'Well, there are lots of good targets in lots of places, but Iraq had nothing to do with it.'"
He said he was so taken aback by the comments, he initially thought Mr Rumsfeld was joking.
US National Security Adviser Condoleezza Rice said she was "flabbergasted" by Mr Clarke's charges, adding that the campaign against al-Qaeda had been the administration's first strategic foreign policy document.
Writing in the Washington Post, she said Mr Bush had acted swiftly after the attacks to secure the country.
White House officials have suggested the allegations may be politically motivated, but BBC correspondent Adam Brookes in Washington says Mr Clarke cannot be swatted aside so easily.
He served in every US administration since Ronald Reagan, before resigning in February 2003.
Later this week the ex-security adviser will go before a special US commission investigating whether the 11 September attacks were preventable.
Our correspondent says if Mr Clarke makes a similar attack on the president at the hearing, it could prove very damaging for the White House.
Mr Clarke helped shape US policy on terrorism under President Reagan and also the first President Bush.
He also worked under President Clinton as his "terrorism tsar" and was then retained by the current President Bush.