US Secretary of State John Kerry said on Saturday the political deal that led to the formation of Afghanistan's national unity government in 2014 had no set expiry date, despite widespread assumptions it will end in September.

Under the terms of the September 2014 agreement, a loya jirga, or special assembly, was expected to be held within two years to amend the constitution. However Kerry, who oversaw the deal that created the government now led by former rivals President Ashraf Ghani and Chief Executive Abdullah Abdullah, said there was no fixed deadline.

"In no way does the agreement itself have some particular termination," Kerry told a joint media conference with Ghani in Kabul.

Referring to discussion about a possible change to plans to cut the number of US troops in Afghanistan from 9,800 to 5,500 by the end of the year, Kerry said US President Barack Obama would be guided by the views of US commanders on the ground.