The explosion occurred at about 1:30 p.m. as the car was on a routine patrol, said Maj. Kevin Arata, a spokesman for the International Security Assistance Force, which is charged with maintaining security in Kabul.
Arata would not release the names or nationalities of the victims, but another ISAF official, speaking on condition of anonymity, said all five soldiers were Canadian.
It was not clear whether the explosion was caused by an old land mine, or one laid recently in an effort to target international peacekeepers.
Afghanistan is among the most heavily mined countries in the world. A German peacekeeper was killed and another wounded in May when their vehicle ran over a land mine apparently left over from decades of war.
Elsewhere, Taliban fighters ambushed and killed 10 government troops and two children traveling with them in southern Afghanistan, a military official said Thursday.
The soldiers killed one of the Taliban attackers and captured another in the fighting about 45 miles north of Kandahar late Wednesday, said Gen. Atta Mohammed, director of Afghan special forces in the region.
Afghan government troops, along with nearly a dozen U.S. forces, were in the area Thursday searching for Taliban rebels, Mohammed said.
Insurgents, believed to be a mix of Taliban rebels, al Qaeda fighters and supporters of renegade warlord Gulbuddin Hekmatyar have been intensifying attacks on government forces and troops from the U.S.-led coalition in recent months.
Peacekeepers have also been targeted.
In June, ISAF suffered its worst-ever hostile casualties when a suicide bomber driving an explosives-laden taxi killed four German peacekeepers and wounded 29 others near the main base in Kabul.
Most recently, assailants on Sept. 11 fired rockets at two bases housing international peacekeepers in the Afghan capital, slightly injuring a Canadian worker.
Four Canadian soldiers died last year in Afghanistan when a U.S. fighter jet mistakenly bombed their position during a live-fire training exercise near Kandahar.
More than 60 Spanish peacekeepers died in May in a plane crash as they returned home after completing their tour of duty in the war-shattered Afghan capital.
NATO took control of the 5,000-strong ISAF force in August and is considering expanding it to regions outside of Kabul. Canadian soldiers make up the largest contingent of the peacekeeping force, with nearly 2,000 soldiers.
Although the plans remain confidential, officials at NATO headquarters in Brussels said they could involve 2,000 to 10,000 more peacekeepers fanning out to major provincial cities.