Kabul (CNN) -- A provincial council candidate and nine of his supporters were killed by the Taliban in Afghanistan two days after they were kidnapped, said Sakhidad Haidari, deputy police chief of northern Sar-e-Pul province.
The 10 were kidnapped Sunday and shot dead Tuesday night, Haidari told CNN on Wednesday.
The bodies of four of those killed, including the Sar-e-Pul election candidate, Hussain Nazari, have been returned to police, he said. The other six remain in the hands of the Taliban.
The Taliban have not commented on the incident, which comes ahead of presidential and provincial elections to be held Saturday.
In a separate incident Wednesday, a suicide bomber blew himself up at the entrance gate to the Interior Ministry in Afghanistan's capital, Kabul, killing six Afghan police officers, Interior Ministry spokesman Sediq Sediqqi said.
The bomber, who was seeking to enter the ministry, triggered his explosive vest when he was identified by police, Sediqqi said.
The Taliban have claimed responsibility for that attack.
Taliban vow to disrupt vote
The violence is the latest to rock Afghanistan in the run-up to the April 5 vote.
There are 11 candidates in the presidential race, with the three main contenders thought to be Abdullah Abdullah, who also ran in the 2009 election, Ashraf Ghani and Zalmai Rassoul.
Outgoing President Hamid Karzai cannot run again because of term limits.
The Taliban have vowed to disrupt the elections and punish anyone involved in them.
But NATO Secretary General Anders Fogh Rasmussen, speaking Wednesday in Belgium, said that the latest briefings from NATO commanders show that despite the Taliban's threats, overall violence across Afghanistan "is lower now than at any time during the last two years."
Rasmussen praised the work of Afghan security forces, which have taken over many responsibilities from the NATO-led International Security Assistance Force, saying they had "demonstrated commitment, courage and professionalism" during preparations for the elections.
"As expected, we have seen a series of attacks including on Kabul today -- an attack which I strongly condemn -- but I welcome that the Afghan people have resisted these intimidation attempts," he said.
He said the country was now looking forward to "historic elections" that would shape its future.
"My message to the women and men of Afghanistan is clear: Go to polls, exercise your democratic rights. Only you have the right to decide your country's future," he said.
Rasmussen said any alleged electoral violations must be investigated swiftly to ensure the elections are credible to all Afghans.
He added that Afghan citizens are registering to vote in "quite high" numbers, despite the Taliban's efforts to disrupt proceedings.
On Saturday, Taliban insurgents attacked Afghanistan's election commission headquarters in Kabul, staff and a government official said. The five assailants were killed, and two people were injured.
A day earlier, five militants set off a car bomb at a guesthouse used by foreigners and then held people as hostages until police killed one of the militants and the other four blew themselves up. A girl was killed in the attack.
On Tuesday, militants stormed an election commission office in Kabul, leading to a five-hour gun battle with Afghan security services. Five people were killed -- two police officers, two election commission workers and a provincial council candidate.
The Taliban claimed responsibility for all three of those attacks.
Journalist Qadir Sediqi reported from Kabul, and CNN's Laura Smith-Spark wrote in London.