Bush on Thursday vowed "we will keep our nerve" in Iraq and hit out at what he branded as "self-defeating pessimism" surrounding a war in which more Americans than ever before are doubting his leadership, according to opinion polls released as the US military death toll nears 2000.
And in remarks seemingly aimed at the Islamic world, Bush said radical groups were "enemies of Islam" and called upon leading Muslim clerics to cleanse their religion of the taint of terrorism.
"The United States and our partners have disrupted at least 10 serious al-Qaida terrorist plots since September 11th, including three al-Qaida plots to attack inside the United States," Bush said.
"We've stopped at least five more al-Qaida efforts to case targets in the United States or infiltrate operatives into our country," Bush said in the speech to the National Endowment for Democracy in Washington.
Bush did not provide details of the targets or of the timing of the foiled strikes.
The president, seeking to reclaim the authority on national security which characterised his first term in office, portrayed al-Qaida as the latest in a long line of ideological threats to freedom and the United States.
Bush tried to rebuff rising anger
over Iraq involvement
"Evil men obsessed with ambition and unburdened by conscience must be taken very seriously and we must stop them before their crimes multiply," Bush said.
"We have seen this kind of shameless cruelty before, in heartless zealotry that led to the gulags and the Cultural Revolution and the Killing Fields."
Aides had styled the speech as an attempt to convince Americans that Iraq was a central front of the anti-terror campaign, and a crucial showdown with Islamic radicalism.
Bush took square aim at critics of his leadership in Iraq, amidst a rising tide of public discontent over the course of the war, growing criticism in Congress and even calls to bring the troops home.
"Observers look at the job ahead and adopt a self-defeating pessimism. It is not justified," Bush said, arguing that Iraq had made "incredible political progress" and warned the idea that America would be better off out of Iraq was a "dangerous illusion".
"In Iraq, there is no peace without victory. We will keep our nerve and we will win that victory," said Bush, who also hit out at critics who say the Iraq war has made America more vulnerable to terrorism not safer.
"The time has come for all responsible Islamic leaders to join in denouncing an ideology that exploits Islam for political ends, and defiles a noble faith"
"I'll remind them that we were not in Iraq on September the 11th, 2001, and al-Qaida attacked us anyway. The hatred of the radicals existed before Iraq was an issue and it will exist after Iraq is no longer an excuse."
In the speech, which also claimed US successes in Afghanistan and in convincing Libya to abandon its weapons of mass destruction, Bush also warned terrorists were exploiting Islam.
"The time has come for all responsible Islamic leaders to join in denouncing an ideology that exploits Islam for political ends, and defiles a noble faith."