Three US soldiers have been shot dead by an Afghan worker at a base in Afghanistan - the second such attack in 24 hours.
The killings took place on Friday at a military base in the Garmsir district of Helmand province in southern Afghanistan.
It happened not far from where three US special forces soldiers were killed by an Afghan policeman earlier that day.
"Let me clearly say that those two incidents clearly do not reflect the overall situation here in Afghanistan," chief coalition spokesman Brigadier-General Gunter Katz told reporters.
However, a statement posted on Twitter by @ABalkhi of the 'Islamic Emirate of Afghanistan' said the attacks were: "clearly summing up mood of Afghan nation towards foreign occupation".
In the latest killings, the soldiers were shot dead by a base employee who turned a gun on them. It was the third such attack in four days.
Military sources said the employee had not been wearing a uniform and it was unclear how he got hold of the weapon.
An Afghan police commander and several of his men killed three US Marines earlier on Friday after inviting them to a dinner to discuss security.
According to Nato, there have been 26 such attacks on foreign troops since January in which 34 people have been killed. Last year, there were 21 attacks in which 35 people died.
'Green on blue' shootings, in which Afghan police or soldiers turn their guns on their Western colleagues, have seriously eroded trust between the allies as Nato combat soldiers prepare to hand over to Afghan forces by 2014, after which most foreign forces will leave the country.
But Brig Gen Katz said the incidents were isolated and were not hurting morale or co-operation between foreign forces and the 350,000-strong Afghan security force.
"We have almost 500,000 police and soldiers working together, side by side, enhancing their trust and enhancing their co-operation in order to fight for a better future for this country," he said.
Violence in Afghanistan is at its fiercest since US led Afghan troops overthrew the Taliban government in 2001.
Last month, an Afghan policeman opened fire on British soldiers in Helmand province, killing three in an attack claimed by the Taliban, and a gunman in uniform killed foreign trainers working for Nato in western Herat province, killing three.