The soldiers were on patrol south of the town of Tirin Kot late on Friday when they came under attack, Lieutenant Colonel Tucker Mansager told reporters in Kabul on Saturday.
"Coalition forces have reported coming under attack overnight south of Tirin Kot. One US marine was killed and one wounded," he said.
"That engagement just ended late last night and early this morning," Mansager added. "It was as the result of a direct fire engagement with anti-coalition militias in the area south of Tirin Kot."
It appears that the marines were part of a new 2000-strong force deployed in Afghanistan to join the hunt for members of the ousted Taliban regime and al-Qaida who are believed active in the south and east of the country.
Four US soldiers have been killed in action since Operation Mountain Storm, the military's latest effort to crush resistance in Afghanistan, began in early March.
An insurgency against foreign forces in Afghanistan and the US-backed government in Kabul has gained momentum in recent weeks, before landmark presidential and parliamentary elections, scheduled for September.
The US-led force in Afghanistan numbers about 20,000. Mansager said the sharp increase from 15,500 troops in recent weeks was because of the marine deployment and a temporary rotation of forces.