Friendly fire incident
An official from the Nato-led International Security Assistance Force (Isaf) said a gun battle broke out when a joint force came under fire on Friday in Wardak in what may have been a "friendly fire incident".
He said only two Afghan soldiers were killed, but it was not immediately clear who fired on them.
"We are working with the ministry of defence to determine the facts of the incident," US Army Lieutenant Nico Melendez, a spokesman for Isaf, said.
The Afghan defence ministry paid tribute to the dead soldiers and condemned Nato's actions.
"After the investigation is completed, the defence ministry wants to bring those responsible to justice," it said in a statement.
In another incident on Friday, Nato forces killed two civilians after opening fire on a taxi as it sped towards a patrol and ignored warnings to stop, in the Gelan district of Ghazni province, the international force said.
Meanwhile, two US soldiers were killed by their Afghan interpreter at a combat outpost in the east of the country.
Nato and Afghan officials said an investigation was still under way but the interpreter was apparently upset over job-related issues.
Also on Saturday, at about 1am, joint Nato-Afghan forces came under attack in the northwestern province of Badghis, prompting a gun battle and an air attack that killed eight fighters, including a group leader, Abdul Jabar Khan, the deputy provincial police chief, said.
The violence in Badghis came a day after Afghan troops, backed by Nato helicopters, clashed with the Taliban in Helmand.
The fighters attacked UN and government buildings in Lashkar Gah, the capital of the southern Afghan province, early on Friday, witnesses and officials said.
The battle lasted eight hours.
Provincial officials said at least five attackers were killed and four Afghan soldiers injured in the fighting.
Qari Yousef Ahmadi, a Taliban spokesman, said seven fighters, armed with suicide vests and machine guns, had been sent to carry out the attack.
He said that 20 foreign and Afghan soldiers were killed or wounded, but Nato said no deaths had been reported on the pro-government side.
Kamal Uddin, the deputy provincial police chief, said no civilian casualties had
The Taliban have attempted similar attacks in Kabul, most recently on January 18 when seven attackers were killed after a five-hour assault.