Since 2002, the United States has allocated more than $68 billion to train and equip Afghan security forces.
A senior US defence official says the decision will also allow greater use of US air power & air support.
Peter Apps says the simple truth is that we tend to look at the Afghan war in entirely the wrong way.
Police are investigating whether there was a 2nd explosion after people rushed to the scene to help.
The US would maintain a force of 9,800 until the end of 2015 while sticking to a 2017 exit plan.
The announcement by US Defense Secretary Ash Carter came ahead of talks at the White House on Tuesday.
The Taliban said they had attacked the foreign guesthouse because they believed it to be a Christian centre.
The violence came as the Taliban steps up attacks ahead of the withdrawal of most foreign troops.
Ashraf Ghani was named president-elect on Sunday after he signed a deal to share power with his opponent.
The operation is one of the single biggest assaults against the Taliban-linked Haqqani network.
The Obama administration has been looking at options for a possible residual US force for months.
The attack in one of Afghanistan’s main cities comes ahead of a presidential election on 5 April.
Barack Obama told Hamid Karzai that he had given the order to the Pentagon for full troop withdrawal.
Hamid Karzai has refused to sign a security deal with the US.
Afghan president Hamid Karzai said on Sunday the United States needed to bring peace.
Taliban intensified its revolt against government in recent weeks.
Taliban has been wreaking havoc, rejecting the elections and vowing to fight until foreign troops leave.
Three people were killed when insurgents attacked the US consulate in western Afghanistan's main city.
