President George W Bush, facing a grim and growing death toll in Iraq, said that threats of more violence by Al Qaeda's second-in-command would not intimidate the United States into retreat.
At the same time, the US military said in Iraq that four more service members had been killed in action, but also insisted American troops were making progress against insurgents.
An AP-Ipsos poll taken early this week showed public support of Bush's handling of the war had dropped to 38%, the lowest so far.
"We will stay the course, we will complete the job in Iraq," Bush said on Thursday in Texas as a videotape by Ayman al-Zawahri, Al Qaeda's No 2, was broadcast around the world.
Al-Zawahri threatened more destruction in London after subway and bus bombings and said in the videotape that the United States would suffer tens of thousands of military dead if it did not withdraw from Iraq.
Bush said that kind of talk only showed why the United States must stay the course.
"They're terrorists and they're killers and they will kill innocent people... so they can impose their dark vision on the world," Bush said as he stood alongside Colombian President Alvaro Uribe who was visiting at Bush's ranch in Texas.
Al-Zawahri's threat was broadcast a day after the deadliest roadside bombing of US troops in Iraq.
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