The poll workers, including two women, were from Britain, the Philippines and Kosovo, government officials said on Thursday.
They were part of a joint UN-Afghan election team handling the 9 October presidential poll.
Seven armed men stopped the UN-marked vehicle the three were travelling in, beat the Afghan driver and pushed them at gunpoint into a pickup truck with tinted windows.
The incident took place in Karteh Parwan, a relatively posh area of the city, close to the Intercontinental hotel.
Akbar Agha, head of a group calling itself the Muslim Army, said in a phone call to Aljazeera's correspondent in Islamabad that his fighters were the ones who seized the three workers for their participation in organising the Afghan elections.
Agha did not set any demands for releasing the foreigners, the correspondent said.