Watch: US troops scramble as Afghan base comes under mortar fire

US soldiers run for cover after rocket strike 0:41

FOB TORKHAM, Afghanistan — U.S. troops at one of the last combat outposts in Afghanistan were preparing to go "outside the wire" and leave the relative safety of their compound when their base came under rocket fire on Friday.

Rifles and flip flops 0:20

The single mortar blast was heard while soldiers were being interviewed by NBC News at Forward Operating Base Torkham, in Nangarhar province, east of Kabul.

The soldiers, immediately sprinted to a concrete bunker, some shouting “go, go, go” and “get down!”

The troops — from 3rd platoon, 230th Charlie Company, 4th Brigade, 10th Mountain Division — huddled inside the bunker, anticipating more fire, before conducting a headcount.

The rocket, which was fired at around 9 a.m. local time (11 p.m. ET Thursday), landed in an open space just outside the outpost. No one was injured.

The same complex came under sustained attack on Sept. 2 this year. That two-hour assault involved suicide bombers, mortars, and small-arms fire.

US troops scramble as rockets strike Afghan base 2:36

NBC News’ Alexander Smith contributed to this report