Ahead of next week's NATO summit in Chicago, the Afghan government has announced the third tranche of the security transition in Afghanistan.

At a press conference in Kabul on Sunday, Ashraf Ghani Ahmadzai, head of the transition commission, said the third phase of the transition will focus specifically on security.

"Security has been taken into serious consideration, but we have serious problem in governance, economic and justice sectors," Ahmadzai said.

The capitals of each of the central-Asian nation's 34 provinces will be among the 120 administrative units that comprise the latest phase of the transition.

Saying the nation is strongly determined to take control of its own affairs, Ahmadzai said this phase, which includes the provinces of Kapisa, Uruzgan and Parwan, will see Afghan forces taking the lead in areas representing 75 per cent of the population of over 30 million people.

In a statement issued after the Sunday afternoon press conference, Barack Obama, the US president, said he welcomed the Kabul government's move to have local forces take control of security in a large new chunk of the country as an "important step forward".