The deputy leader of al-Qaeda, Ayman al-Zawahiri, has said the decision of UK forces to "flee" Basra shows that Iraqi insurgents are gaining strength.
In a web-posted interview, Egyptian-born Mr Zawahiri said the US-led coalition was "defeated and looking for a way out" of Iraq.
Iraq took formal responsibility for security in Basra province on Sunday.
The 4,500 British troops still in Iraq will now take a backseat role, focusing on training local security forces.
The move to Provincial Iraqi Control four-and-a-half years after the invasion is being seen as a key stage towards a final British withdrawal from the country.
Speaking in a 90-minute interview with al-Qaeda's media arm, al-Sahab, Zawahiri said the world was witnessing a "triple failure for the Americans in Iraq".
"No matter how much the gigantic propaganda machine in America tries
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