The US commander in Afghanistan told lawmakers Thursday he had proposed "options" to the White House that would slow the pace of a planned withdrawal of American troops from the country.

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.

"I have provided options on adjusting our force posture through my chain of command," Campbell said.

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.

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.

"A group of us met with President Ghani over the weekend, and he was very strong and adamant that this current plan will put the nation in danger," McCain said.

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.

There are 10,600 American troops in the 13,000-strong coalition force currently on the ground.

- IS in Afghanistan? -

Lawmakers at the hearing also raised concerns about Islamic State jihadists possibly gaining a foothold in Afghanistan.

Campbell said the IS group, or Daesh, had a "nascent" presence that appeared to be "more of a rebranding of a few marginalized Taliban."

"But we're still taking this potential threat, with its dangerous rhetoric and ideology, very, very seriously."

Although the White House has touted the end of "combat operations" in Afghanistan, US and Afghan special operations have stepped up secret raids against Taliban and Al-Qaeda in recent months, according to the New York Times.

The expanded operations are based on valuable intelligence from a laptop computer and files seized in a raid in October on an Al-Qaeda leader, according to the New York Times.

The increase in raids also was a result of a new bilateral security agreement signed last year by the new Afghan president. The deal softened restrictions on night raids by American and Afghan forces that had been imposed by the former president, Hamid Karzai, the newspaper reported.