The new Afghan government has signed a security deal with American officials that will allow US troops to remain in the country beyond 2014.
The agreement was signed by Afghanistan's newly appointed national security adviser, Hanif Atmar.
The previous president, Hamid Karzai, refused to sign the bilateral security agreement (BSA) with the US, which strained ties between Kabul and Afghanistan.
Most NATO forces are to withdraw this year, leaving 9,800 US troops behind, the BBC reported.
The total number of troops in the US-led mission at the start of next year will be around 12,500, with the remainder coming from allies such as Germany and Italy.
US ambassador to Kabul Jim Cunningham signed the long-delayed agreement on behalf of the government in Washington.
The BSA allows for some foreign special forces to stay in the country to conduct "counter-terror operations" and others to support and train Afghan forces.
The US deployment will be halved by the end of 2015 and withdrawn almost completely by the end of 2016. The Associated Press reports that the US plans to leave about 1,000 troops in a "security office" after this deadline.
NATO countries have been steadily reducing the number of troops they have committed to the Afghan mission, handing over control to local security forces.
Earlier this year, there were estimated to be just over 50,000 NATO troops serving in Afghanistan from 49 contributing nations. Of these the bulk - about 34,000 - were US troops.
Ghani was sworn in as Afghanistan's new president on Monday, replacing Karzai.
The Kabul ceremony followed six months of deadlock amid a bitter dispute over electoral fraud and a recount of votes.
Under a US-brokered deal Ghani shares power with runner-up Abdullah Abdullah who becomes chief executive.
"The signing [of the BSA] sends the message that President Ghani fulfils his commitments," Daoud Sultanzoy, an aide to Ghani, told AFP. "He promised it would be signed the day after inauguration, and it will be."
> Karzai's Refusal
Over the past years, Karzai has been sharply denouncing the United States for the deaths of Afghan civilians in airstrikes and for holding suspected Afghan militants prisoner without trial. He also opposed US overtures to the Taliban, and repeatedly condemned US searches of Afghan homes. He was particularly upset about a November 19 night raid in which twin brothers in a Nangarhar Province town were a unilateral US strike, as Afghan officials claim.
In a farewell speech marking his departure from the Afghan presidency post on Tuesday, he blamed the United States for his country’s long war..
“One of the reasons was that the Americans did not want peace because they had their own agenda and objectives,” Karzai said.
The number of US service personnel in Afghanistan peaked at about 101,000 in 2011, boosting the total of the NATO force to about 140,000.
But an extra 33,000 American soldiers sent as part of a "surge" were withdrawn in 2012, and Washington has carried on winding down combat operations since then.
