London, England (CNN) -- The security relationship between the United States and Britain is closer than at any time since World War II, the head of the U.S. Central Command said Wednesday.
Gen. David Petraeus was speaking at a conference here at the Royal United Services Institute, where he said Britain has played an "irreplaceable" role in Iraq, and a similar role in Afghanistan.
"It's clear that, as was the case in Iraq, the scale of the British contribution in Afghanistan is such that the coalition cannot succeed without you," Petraeus told the British audience.
The alliance between the United States and Britain formed the "core" of the coalition in Iraq from the beginning, he said. The cooperation included the British SAS, or special forces, which were "fully integrated" into U.S. special operations teams, Petraeus said.
The SAS led in a number of the most important counterterrorism operations of the war, he said.
Now that the two countries have worked together for five years in Iraq and eight in Afghanistan, there is a generation of officers and enlisted service members "for whom coalition operations are the norm," Petraeus said.
He said the relationship should be formally incorporated into British and American organizations and procedures, with more combined assignments.
"It is one thing to deploy our people to combat zones and have them adapt to coalition operations and build effective teams, which they've shown they can do amazingly well," he said. "But it's quite another thing to move beyond the ad hoc -- to instill the coalition mindset by building partnerships and personal relationships through our training and education programs before our units deploy and then to sustain them once the deployment is over."