"We can't run the peace talks; we can't settle this from the outside", he said.
Ghani's government called for a ten-day ceasefire in June to coincide with the Muslim holiday of Eid.
The US-led coalition headquarters in Kabul has confirmed that a US service member has been killed in an apparent insider attack in southern Afghanistan.
The so-called "green-on-blue" attack is the latest in a line of incidents where Afghan soldiers have turned their weapons on worldwide forces they are working with. No other details of the attack were available.
Green-on-blue or insider attacks, in which a member of the ANSF attacks American service members, have taken place every year since 2008.
Attacks by Afghan security forces against coalition troops working alongside them were common in Afghanistan several years ago, when the Pentagon had more than 100,000 personnel deployed there. It was claimed by the Taliban.
Some of the USA forces are involved in counterterrorism operations, particularly against the local Islamic State group.
The latest incident comes as Lieutenant General Scott Miller is set to become the next commander of US and North Atlantic Treaty Organisation forces in Afghanistan.
The success of this operation could put the Trump administration in a position to signal that one of its vital objectives in Afghanistan has been met, namely smashing the Islamic State.