The coalition's International Security Assistance Force (ISAF) issued a statement saying five NATO soldiers had been killed in an insurgent attack in the east of the country, later confirming that the incident was in Kapisa.
The police chief in the district of Tagab in Kapisa said a suicide bomber had detonated in front of a French military convoy in the area, leaving "some casualties among the French forces".
"At around 11:25 today a suicide attacker on foot targeted a French convoy in Gulzarkhail village of Tagab district. There were some casualties among the French forces," said senior police official Sayed Sakhidad Matin.
He said an Afghan policeman had also been injured in the attack.
The office of French President Nicolas Sarkozy -- who paid a surprise visit to the war-torn country a day earlier -- later confirmed five French soldiers had died in the attack and said an Afghan civilian had also been killed.
Four more soldiers and three more local civilians were "gravely wounded" in the attack on a unit which was protecting a local tribal council meeting, the presidential statement said.
"A terrorist detonated his bomb close to the French soldiers," the Elysee said, condemning the "cowardly murder" and expressing France's determination to remain part of the NATO-led coalition fighting in Afghanistan.
The attack was the deadliest blow to French forces in Afghanistan since August 2008, when 10 soldiers were killed and 21 injured when a patrol was ambushed by Taliban guerrillas in the Sarobi district east of Kabul.
The deaths brought to 69 the number of French soldiers to have died in Afghanistan since 2001, when they deployed in support of the US-led campaign to overthrow the Taliban regime and hunt Al-Qaeda militants.
They are also a political blow for Sarkozy, coming a day after his visit to Afghanistan -- where he defended the campaign against opposition at home -- and the day before the Bastille Day military parade in Paris.
The march down the Champs Elysees is the highlight of the French army's calendar, but will now be overshadowed by the ongoing violence in Afghanistan, amid calls for France to accelerate its withdrawal from the country.
Sarkozy announced on Tuesday during his trip to Sarobi that a quarter of France's 4,000-strong contingent would come home before the end of next year.
NATO earlier announced the death of two foreign troops in the south, one in an insurgent attack on Wednesday, and a second in a bomb attack on Tuesday.
The latest deaths bring this year's toll to 306 foreign troops killed in Afghanistan, according to an AFP estimate based on data compiled by independent icasualties.org.