Elsewhere, five civilians and an Afghan election staff member was killed in the latest violence to hit the country ahead of next month's polls.
"A group of 50 terrorists attacked a checkpost in Kamdesh district of Nuristan province in which four soldiers and four police were killed yesterday evening," interior ministry spokesman Lutf Allah Mashal said on Wednesday.
The checkpoint, about 220km northeast of the capital Kabul, came under fire late on Tuesday night the spokesman said.
Separately, five civilians were reportedly killed by US forces on Tuesday in a part of eastern Laghman province where a roadside bomb blast had targeted a US military convoy.
An Afghan official, who asked not to be named, said US forces had shot dead the civilians and added that "one of the five was a woman, and it took place in Ali Shing district of Laghman province."
The accusation could not be independently verified and a spokesman for the US-led coalition, Lieutenant Colonel Jerry O'Hara, said: "We don't have such a report".
Mashal said: "I can confirm that five civilians were killed in a shootout in Laghman province yesterday, but it is not yet clear how the shootout took place or if coalition forces were involved".
Also on Tuesday, an Afghan election worker was shot dead in the country's south, an official said.
Election worker killed
Armed men on a motorcycle killed Abd al-Qayoom, who worked for the Joint Electoral Management Body, said Helmand deputy governor Haji Mohayudin and election officials in Kandahar.
"I can confirm that five civilians were killed in a shootout in Laghman province yesterday, but it is not yet clear how the shootout took place or if coalition forces were involved"
Lutf Allah Mashal,
Afghan interior ministry spokesman
Four suspects had been arrested after the election worker's killing in Lashkar Gah, Helmand province, 550km south of Kabul, said Mohayudin.
Last month an Afghan electoral worker was shot dead in Paktika province and his son wounded.
In a clash on Monday, Afghan police who came under attack said one of the attackers were wounded and that they had arrested two more and seized a weapons depot in Orgun district of southeastern Paktika province, according to US-led forces.
Police found bomb-making material, hand grenades, parts of rocket-propelled grenades and ammunition for machine guns and AK-47 assault rifles during a raid on a compound where the attackers fled, said the statement.
Mashal also said 30 Taliban fighters and their provincial level commander, Mullah Abdul Bari, had surrendered to the Afghan government in the Shar-e-Safa district of southern Zabul province on Wednesday.
Dozens of former Taliban and other fighters have given up their weapons after US-backed President Hamid Karzai last year announced an amnesty to all fighters.