In the northern province of Kunduz, eight family members of a local anti-Taliban commander died in an ambush.
Elsewhere, six members of two different campaign teams and a police officer were killed in bomb attacks.
Taliban militants, who have vowed to disrupt Saturday's polls, have been blamed for a recent surge in violence.
Two days ago, the Kabul headquarters of the Independent Election Commission (IEC) was attacked.
Five militants took over a nearby building and targeted the commission with rocket-propelled grenades and heavy machine-guns.
The assailants were eventually killed by Afghan security forces.
The anti-Taliban militia commander apparently targeted in Kunduz on Monday, Mohammad Omar, was not in the vehicle with his family when a roadside bomb exploded beside it.
Officials said his two sons and a brother were among the dead.
In the province of Sar-i-Pul, to the west, four Afghan police officers were killed during an offensive against the Taliban.
Gunmen also kidnapped a provincial council candidate and 10 of his entourage, Sar-i-Pul Governor Abdul Jabar Haqbeen said.
They did not have any security protection and were returning after campaigning when they were   kidnapped by the Taliban, he added.
The governor said troops were ready to carry out a rescue operation, but that local elders had said they wanted to give negotiations a chance.
Eighteen people have been killed in a series of attacks in Afghanistan, officials say, as it prepares for presidential and provincial elections.