A suicide attacker targeted a NATO convoy in Kabul on Sunday, killing four civilians and wounding at least 35 others, officials said, in the latest violence to hit the capital as politicians wrangle over election results.
The NATO force made no immediate comment on the attack, which came as foreign troops rapidly wind down combat operations at the end of a 13-year war against Taliban insurgents.
"Two children, a woman and a man were killed and 35 others were wounded in the attack," a statement from Kabul police said.
"Foreign forces vehicles were partially damaged but, according to our initial information, there were no casualties to them."
A spokesman for the Taliban said the insurgents claimed responsibility for the attack.
Ahmad Shah, a shopkeeper at the scene, told AFP: "I saw several people covered in blood around the area. The blast was huge, our windows are shattered.
"Several vehicles were damaged."
US-led foreign troop numbers in Afghanistan have declined from a peak of 150,000 in 2012 to just 44,300 now.
All NATO combat soldiers will depart by the end of the year, though a follow-up support mission of about 10,000 troops is planned if the next president signs security deals with the US and NATO.
Afghanistan's two rival presidential candidates signed a deal on Friday to form a national unity government, opening an apparent way forward in a bitter dispute over the election that threatens to revive ethnic conflict.
Ashraf Ghani and Abdullah Abdullah vowed to work together — whoever becomes president — after an ongoing audit of all eight million votes finally declares the winner of the June 14 election.
The risk of spiralling instability has loomed large in Afghanistan since Abdullah refused to accept preliminary results that put Ghani ahead, accusing his rival of stealing the election by massive ballot-box stuffing.
The dangers of international military intervention were underlined on Tuesday when a rogue Afghan soldier shot dead a US general at an army training centre in Kabul, wounding more than a dozen others including a senior German officer.
Karzai, who has been Afghan president since the Taliban regime was ousted in 2001, has called for the inauguration of his successor within weeks, saying uncertainty was damaging the nation's fragile security and economy.
Taliban insurgents have launched new offensives in the south and east in recent months, and violence is increasing across the country according to several independent reports.
Earlier this month, a Taliban suicide bomber in Kabul killed eight military officers in an attack on an air force bus.