There is no fixed date for an end to the power-sharing deal between rival Afghan leaders, said US Secretary of State John Kerry on a visit to Kabul.
The assumption had been that the national unity government formed by Ashraf Ghani and Abdullah Abdullah would finish in September.
Mr Kerry brokered the deal after disputed election results.
As he flew out of the country, several explosions rang out in the city’s diplomatic area.
After the deal, there were expectations that a Loya Jirga, a special assembly of elders, would be convened within two years to amend the constitution and create the post of an executive prime minister.
During his visit, Mr Kerry held meetings with Mr Ghani and the country’s Chief Executive Mr Abdullah.
Mr Ghani said they all hoped the Taliban would engage in peace talks and craft “a legitimate process that brings an end to violence.”
At least two explosions as well gunshots were heard in Kabul’s diplomatic area as Mr Kerry’s plane was preparing to take off.
The Taliban have previously attacked prominent official and foreign targets in the Afghan capital.
Mr Kerry’s visit came at a time when Nato forces are increasingly being deployed in battle zones to support Afghan forces fighting the Taliban.
Last year, the number of people killed and wounded in conflict in Afghanistan rose to the highest level yet recorded, the UN said.