The two Swedish soldiers, Johan Palmlöv and Gunnar Andersson, and their Afghan interpreter, Mohammad Shahab Ayouby, were part of the patrol which came under fire near a police station, 40 kilometres west of Mazar-e Sharif, near the village of Gurgi Tappeh.
Soldiers in the patrol have confirmed that their attacker was dressed in an Afghan police officer's uniform.
"A military police investigation has been launched to clarify the circumstances. It is still too early to determine if it was a police officer or an attacker dressed in a police uniform," said Gustaf Wallerfelt at the FS 18 contingent stationed in the area, in a Swedish military statement.
"The investigation is being conducted in close cooperation with the Afghan police."
It has been confirmed that the two dead Swedish officers come from the Stockholm area and have been named as 28-year-old Captain Johan Palmlöv and 31-year-old Lieutenant Gunnar Andersson.
The third Swedish soldier, who sustained minor injuries in the attack, is also from the Stockholm area.
The Swedish soldiers were operating in an area where Swedish and Finnish peace keepers confiscated 70 kilogrammes of narcotics and a quantity of explosives earlier in the week.
According to news agency TT reporters in the area, villagers believe that the soldiers could have been attacked as an act of revenge from local Taliban.
The use of police and army uniforms is a common method applied by opponents to the presence of foreign troops in Afghanistan to carry out suicide attacks or to gain access to security zones.
The investigation into the identity of the attacker, who was killed in return fire, is likely to take time, the Swedish military have confirmed.
A commission of inquiry has been assembled in Stockholm and will be despatched to Mazar-e Sharif at the earliest opportunity to assist with inquiries.
Swedish forces have been operating in Afghanistan since 2002.
The 500-strong Swedish ISAF-led force (FS18) is based in Mazar-e Sharif, 400 kilometres northwest of Kabul.
ISAF is a NATO-led security and development mission in Afghanistan established by the United Nations Security Council in 2001. The base is home to Swedish and Finnish peacekeeping forces.
"There remains a belief that we can achieve our goal, if for no other reason everything would have been in vain," Gustaf Wallerfelt said of the atmosphere among Swedish forces in Afghanistan.