"At this time, we believe they were abducted by terrorists belonging to al-Qaeda or an affiliated group," Major-General William Caldwell, the chief US military spokesman in Iraq, said in a statement.
Caldwell said that a manhunt involving 4,000 US troops backed by jets, helicopters, sniffer dogs and spy satellites would continue until the three are found.
"I cannot promise you that these efforts will produce the results we all are praying for," he said.
"But what I can promise you the American people, and particularly the families of these missing men, is that we are doing everything we can to find these brave and courageous soldiers."
Danish death
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| Danish troops are mainly based near Iraq's southern city of Basra [AFP] |
The Danish military said on Monday that one of its soldiers had died after his vehicle was struck by a roadside bomb in southern Iraq.
Five other soldiers and an Iraqi interpreter were also wounded in the attack the army said.
The soldier was the seventh Danish serviceman to die in Iraq.
Denmark has about 470 troops in Iraq, mainly stationed near the southern city of Basra.
Anders Fogh Rasmussen, the Danish prime minister, announced in February that he would withdraw the troops in August.
They are to be replaced by a unit of four helicopters and 50 men, who will work alongside the British until December.