Mr Gates recently reaffirmed his commitment to provide extra troops
US Defence Secretary Robert Gates has ordered the deployment of an additional combat aviation brigade to Afghanistan early next year, officials have said.
The decision to send about 2,800 soldiers, equipped with both attack and transport helicopters, comes as part of an effort to counter the insurgency.
Three or four combat brigades are to follow in late spring or early summer.
The top US and Nato commander in Afghanistan, Gen David McKiernan, has requested at least 20,000 extra troops.
There are currently 31,000 US troops in the country, 14,000 of whom are part of the 51,000-strong Nato-led International Security Assistance Force (Isaf).
The US army combat aviation brigade, which includes Apache attack helicopters as well as Black Hawk and Chinook aircraft, is expected to move from the US in early spring.
It is considered a support force and does not fill the need for the four combat brigades requested by Gen McKiernan, officials say.
During a visit to Kandahar last week, Mr Gates said the US military's primary goal was to build up the Afghan security forces so they become capable of operating more independently, but warned that this might take several years.
"This is a long fight, and I think we're in it until we are successful along with the Afghan people," he said.
"I do believe there will be a requirement for sustained commitment here for some protracted period of time. How many years that is, and how many troops that is I think nobody knows at this point."
But in an interview on Wednesday, Mr Gates said that the US "should think long and hard" before sending significantly more than the 20,000 additional troops requested by Gen McKiernan so they do not become to be seen as an occupying force.