A group of Taliban descended from mountain hideouts in Helmand province and attacked the post in Sangin district late on Wednesday.
"A couple of tents, some food stuff, a vehicle and weapons were found at their base but the Taliban managed to escape," Muhammad Wali, a spokesman for the Helmand administration, said from the provincial capital Lashkargah, 550km southwest of Kabul.
South and southeast Afghanistan have borne the brunt of a rise in violence blamed on a resurgent Taliban who have increasingly targeted aid workers as well as Afghan militia forces and US troops.
Wave of attacks
A French UN worker was shot dead on Sunday in the middle of the southeast town of Ghazni by two suspected Taliban who were later arrested.
The killing of Bettina Goislard, 29, prompted the UN refugee agency she worked for to withdraw its 30 foreign staff from the south and east and suspend assistance to refugees returning from Pakistan.
A wave of attacks targeting humanitarian workers has forced the suspension of aid projects across vast swathes of the south and southeast Afghanistan, undermining post-war reconstruction.