In an unannounced but already scheduled visit, US Defense Secretary Leon Panetta landed in southern Afghanistan on Wednesday at the Camp Bastion military base. The trip comes in the wake of Sunday's shooting spree that left 16 Afghans dead, most of them women and children.
Tensions were running high a day after suspected Taliban insurgents opened fire on an Afghan government delegation attending a memorial service for the civilians who were murdered.
The hail of gunfire left one member of the Afghan security forces dead and one policeman wounded.
Panetta was due to meet President Hamid Karzai and local leaders in the south in a bid to reassure Afghans after Sunday's horrific violence when a US Army sergeant allegedly went house to house killing Afghans in the Panjwayi district of southern Kandahar province.
The shooting marked the latest in a string of damaging incidents that have raised questions about the NATO war effort, including the burning of Korans at an American base that triggered violent unrest in which around 40 people were killed.
Panetta's visit coincides with a growing debate in Washington about the course of the 10-year-old war, with some sceptics in and outside the White House arguing for an accelerated drawdown of troops.
Under current plans, the United States aims to reduce the force of nearly 90,000 to about 68,000 by the end of September, with most of the remaining combat troops due to be pulled out by the end of 2014.
US officials have left the door open to a smaller follow-on force after 2014 but the spate of recent setbacks has complicated negotiations with the Afghan government for a long-term security agreement.
On Monday, Panetta portrayed the shooting rampage as an isolated incident and insisted the US-led war effort was on track, with Taliban insurgents on the retreat.
He told reporters that "we cannot allow these events to undermine our strategy or the mission that we're involved in".
"It's important that we push on, and that we bring this war to a responsible end and achieve the mission that all of us are embarked on," he said.
Karzai has described the massacre as "unforgivable"; while US President Barack Obama Tuesday said he had assured the Afghan president that "the United States takes this as seriously as if it was our own citizens and our own children who were murdered".
Obama promised that the culprit would face the "full force" of US law, wherever the investigation led.