By early morning, tens of thousands of members of the Hazara ethnic community had gathered in the west of Kabul to march toward the presidential palace, organisers said.
Overnight, police had moved containers and concrete pylons into the commercial center of the capital and were preventing cars and pedestrians from entering.
Main intersections and access roads were all closed, the usual peak hour traffic jams were nonexistent, and most shops remained shuttered.
Armed police and rapid reaction forces took positions across the capital, with some corners covered with makeshift machine-gun posts.
Authorities told protest organisers that the march would be confined to a route that would not take them near the presidential palace, fearing a repeat of a November demonstration by Hazaras that turned violent. Daud Naji, a protest leader, said the Hazaras were calling for the multimillion-dollar electricity line to be routed through Bamiyan province, in Afghanistan's central highlands, where most of the country's Hazaras live.
The original plan routed the so-called TUTAP line through Bamiyan, but was changed in 2013 by the previous government, which routed it through the narrow Salang Pass, in Parwan province, east of Bamiyan.
The plan was inaugurated in Tajikistan last week by leaders of Turkmenistan, Uzbekistan, Tajikistan, Afghanistan and Pakistan, the countries that will benefit from the 500 kV of power it should eventually generate. The plan, backed by the Asian Development Bank, is already six months behind schedule.