Gordon Brown says Britain will host an international conference on Afghanistan next year to outline conditions for handing security responsibilities back to Afghan authorities.
A statement from Mr. Brown's office includes a nine-month timeline with key security goals for Afghan President Hamid Karzai.
It calls for the Afghan government to build up the country's army, police and local governance so control of the country can be given to local authorities, and British troops can withdraw.
Mr. Ban said another conference would be held in the Afghan capital, Kabul, a few months after the London meeting.
In other developments, Afghan police say 12 prisoners have escaped from a prison in western Afghanistan.
Police said Saturday the inmates broke out of the prison in Farah province by digging a tunnel from their cell to the outside. Officials captured a 13th prisoner as he tried to escape.
In the northern province of Takhar, police say gunmen attacked and killed the provincial head of the Red Crescent organization Friday.
At least three suspects have been detained for the murder.
Local officials have suggested that the killing may have been prompted by a personal conflict, and was not related to the man's work.
And in the Afghan capital, Kabul, Saturday, security officials said a bomb in a trash can exploded in the city's center, causing little damage and no injuries.
U.S. military officials have called for allied nations to send up to 10,000 additional troops, as U.S. President Barack Obama prepares to send more American soldiers.
News reports say Mr. Obama is most likely to call for the deployment of at least 30,000 more U.S. troops to add to the 68,000 U.S. troops already in Afghanistan.