General John Campbell, who oversees 13,000 US and allied troops, said he had taken into account a request from Afghan President Ashraf Ghani to revise President Barack Obama's plan to pull out all US combat troops by the end of 2016.
"He (Ghani) has asked for NATO and the United States to provide some flexibility in our planning to account for the fact that his government remains in transition," Campbell told the Senate Armed Services Committee.
The US Army general said Washington had to decide how long to keep troops at bases in the north or south before consolidating the force in the capital Kabul.
"The issue is how long we stay engaged at the regional level in the transition year of 2015," he said.
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Asked by Senator John McCain, chairman of the committee, if he supported the options to push back the withdrawal timeline, Campbell said: "Yes, absolutely."
McCain has been a fierce critic of Obama's plan to pull out troops, saying that the decision has been driven by politics instead of security conditions on the ground.
Obama and his fellow Democrats in Congress are anxious to wrap up the US military role in Afghanistan after a 13-year-old war that has left more than 2,000 American troops dead and some 20,000 wounded.
But amid concerns over a resurgent Taliban, the Obama administration has already adjusted its drawdown plan. In December, officials announced that an additional 1,000 US troops would remain in Afghanistan in 2015 to meet a shortfall of NATO forces.