Two Finnish aid workers were shot dead in the centre of Herat, western Afghanistan, on Thursday hours after a marketplace bomb killed at least six people in the northern province of Takhar.
The attacks came at a time of heavy violence and political tension, as election officials preside over a painfully slow recount of contested ballots in a fraud-plagued presidential poll.
Civilian casualties climbed to record levels in the first six months of this year, UN figures showed, as insurgents test the security forces in the wake of Nato troop drawdowns.
The aid workers were travelling in a local taxi when their attacker pulled up beside them, riding pillion on a motorbike, and shot the two women through the window.
"They were travelling to their office when they were attacked in the Shar-e Nau area of Herat," said provincial governor Fazlullah Wahidi. "An investigation is now under way."
The taxi driver and a colleague in the front seat were arrested, Herat police chief Abdul Rauf Ahmadi said. The Taliban declined to claim responsibility for the attack, saying they were still investigating.
"The barbaric fate of the women affects us all. The act is particularly shocking as the women were in Afghanistan to help local people," Finnish president Sauli Niinistö said in a statement. He also demanded that the killers be brought to justice.
The women worked for a well-respected Christian organisation, International Assistance Mission, which has been active in Afghanistan since 1966, providing medical aid, education and economic support.
Despite its religious background, the group only does development work; proselytising is forbidden in Afghanistan, where the penalty for converting from Islam is death.
Several other IAM employees were killed in a 2010 attack on a medical convoy in northern Badakhshan, when British doctor Karen Woo also died.
The marketplace bomb was attached to a motorbike and aimed at a police car, AP reported, but detonated when only civilians were in the area. As well as six killed, another 26 were injured, several of them children.
The Taliban did not claim responsibility for either attack, saying only that they were investigating the shootings in Herat.
Also on Thursday, a suicide bomber hit a checkpoint in eastern Nangarhar province, killing a local police commander and his bodyguard. Security has declined in many parts of Afghanistan, with a rise in crimes such as kidnapping and robbery as well as insurgent attacks.
The Taliban traditionally step up attacks during the summer "fighting season", when snow-melt and vegetation growth make it easier for soldiers to slip over mountain passes from safe havens in neighbouring Pakistan, and conceal themselves and weapons in Afghanistan.