Lieutenant General Ricardo Sanchez, the commander of the US-led occupation's ground forces in Iraq, was speaking after the capture of Pakistani al-Qaida suspect Hasan Guhl.
"For months I've been saying that al-Qaida fingerprints have been here in Iraq. The capture of Guhl is pretty strong proof that al-Qaida is trying to gain a foothold here to continue its murderous campaign.
"The capture is great news for both Iraqis, the coalition and for the international community's war against terror," Sanchez said.
Guhl was captured last Thursday near northern Iraq's border with Iran.
US officials believe he has worked in the past with captured al-Qaida leader Khalid Sheikh Muhammad, and had connections to people involved in the bombings of US embassies in east Africa.
Sanchez said the al-Qaida presence in Iraq dated back at least as far as a 12 November truck bombing in the southern city of Nasiriyah that killed 28 people, including 19 Italian soldiers.
US soldiers come under daily
attack in Iraq
He said the organisation, blamed by the US for the September 11 attacks, was adapting to the Iraqi environment and joining forces with elements from the former regime of Saddam Hussein.
Sanchez has previously said fighters trained and financed by al-Qaida were trickling into Iraq from Syria to aid the resistance to the US occupation.
"Foreign fighters continue to come into the country, but they are coming in small numbers," he said in an interview earlier this month.
He said foreigners were "the ones that are driving the politically-born improvised explosive devices for the most part".
The US often blames resistance attacks against occupation targets on Saddam loyalists or al-Qaida fighters.
However, some analysts believe this is a convienient way of hiding the fact that the Iraqi resistance is widely supported by the local population.