US officials have identified the soldier accused of killing 16 Afghan civilians a week ago as 38-year-old Staff Sergeant Robert Bales. Meanwhile, a former German military chief of staff says the Afghan mission is futile.
The murders in southern Kandahar province were the latest in a series of incidents that have angered Afghans and intensified resentment toward US-led troops in the country.
Many Afghans are demanding Bales face charges in Afghanistan, but according to reports he has already been removed from the country and taken to Kuwait before his eventual transfer to the US military prison at Fort Leavenworth, Kansas.
Bale's lawyer said his client had been upset by a serious injury to a fellow soldier a day earlier, but that he held no animosity toward Muslims.
A US official told news agency AFP on condition of anonymity that "investigators have reason to believe that alcohol may have been a factor in this tragic accident."
Afghan President Hamid Karzai lashed out at the US earlier on Friday for failing to cooperate fully with the investigation into the massacre. He also questioned whether Bales could really have acted alone.
"This has been going on for too long. You have heard me before. It is by all means the end of the rope here," Karzai told reporters.
Discussions over pullout
Meanwhile, Karzai spoke with US President Barack Obama by telephone on Friday, with the pair reiterating previous pledges to ensure American troops would be pulled out of Afghanistan by the end of 2014.
The two leaders reaffirmed that they were committed to the agreed timetable "in which Afghan forces would complete the process of transition and have full responsibility for security across the country by the end of 2014," the statement read.
The Afghan leader's office also released a statement saying that "the two leaders took the opportunity to reaffirm our shared commitment to the Lisbon framework," which calls for a transfer of responsibility to Afghan security forces in 2014.
"They also agreed to further discuss concerns voiced by President Karzai about the presence of foreign troops in Afghan villages," the statement said.
Meanwhile, in an interview with the German daily newspaper Mitteldeutsche Zeitung, former German military chief of staff Harald Kujat siad that he felt the Afghanistan mission had become futile. "We have made enough sacrifices and we have done enough," said Kujat.
"When you are no longer welcome then, at some time or another, you have to go. I have nothing against an early withdrawal."
dfm, ng, rc /ch (AFP, AP, dpa)