The US president Mr George W Bush has condemned this week's suicide bombing attacks in Jerusalem and Baghdad on Saturday as part of militant campaigns to impose a "totalitarian vision."
"These two bombings reveal, once again, the nature of the terrorists, and why they must be defeated," Bush said in his weekly radio address, which was prerecorded.
"Terrorists commit atrocities because they want the civilized world to flinch and retreat so they can impose their totalitarian vision," Mr Bush said.
He said the two bombings were attacks in a war against "every free nation and all our citizens." He vowed to keep fighting and prevail.
A bombing at UN headquarters in Baghdad on Tuesday killed up to 24 people, including UN Iraq envoy Sergio Vieira de Mello. The Jerusalem bus bombing, for which the Palestinian militant group Hamas claimed responsibility, killed 20.
The attacks dealt a blow to Bush's attempts to promote stability across the Middle East following the US-led war to oust Iraqi President Saddam Hussein.
The bombing in Iraq fueled speculation the US occupation is facing an influx of Muslim fundamentalist militants sympathetic to al Qaeda leader Osama bin Laden.
Mr Bush said on Friday "al Qaeda-type fighters" were now opposing the occupation in Iraq.
Despite the Baghdad attack and ongoing killings of US soldiers, Mr Bush said in his radio address that most of Iraq was moving steadily toward reconstruction and self-governance.
"This progress makes the remaining terrorists even more desperate and willing to lash out against symbols of order and hope, like coalition forces and UN personnel," he said.
"The world will not be intimidated. A violent few will not determine the future of Iraq."
Similarly, he said "murderers" would not decide the future of the Middle East. "A Palestinian state will never be built on a foundation of violence."