KABUL, Afghanistan -- Six of the eight American, British and coalition service members killed since Thursday in southern Afghanistan were shot in the company of their Afghan allies, officials of the NATO-led coalition here said Saturday.
The killings heightened worries about how the coalition troops, who are training members of the Afghan Army and the police, can protect themselves while working at close quarters with their Afghan counterparts. Afghan and NATO officials said they were examining the extent to which the attacks by Afghans in positions of trust were part of a concerted Taliban strategy to disrupt the coalition's operations.
"We take all of these incidents seriously, and force protection is paramount on our minds," said James Graybeal, a spokesman for the NATO-led military coalition here.
"While these incidents are a challenge, it's important not to lose sight of the fact that more than 330,000 A.N.S.F. members are doing their jobs professionally every day, and that results in tens of thousands of interactions with coalition troops that are positive and involve great rapport," he said, referring to the Afghan National Security Forces.
An Afghan security official with extensive knowledge of southern Afghanistan said the tactic of using assailants embedded in the army or police forces to kill their coalition partners was a particularly worrisome one and had become one of the three main Taliban tactics.
"This is one of the dangerous and bad tactics that the Taliban have started to use," said the official, Asadullah Khalid, the border and tribal affairs minister, who is also the security chief for southern Afghanistan. "Because they cannot fight us face to face, they are using I.E.D.'s, suicide bombings and this kind of attack."
Mr. Khalid said he believed that in the effort to increase the size of the army and the police, the forces grew "too much, too fast" to allow for thorough vetting of recruits.
A similar attack on Saturday took the lives of 10 Afghan police officers in Delaram, a district of Nimruz Province in southwestern Afghanistan. An Afghan policeman turned his gun on 10 officers before he was killed by others, said Abdul Karim Barahavi, the Nimruz governor.
"The 10 policemen who were killed were sitting in a room which was their guard post at the edge of the district center," Mr. Barahavi said. "They died on the spot."
Among the dead was the platoon commander, he added.
Three coalition soldiers killed on Friday were shot at the district police headquarters in Garmsir in Helmand Province. The headquarters shares or is next to a compound with a coalition base. It is also the site of the district governor's compound, according to local officials.
Little is known so far about the gunman, but a preliminary investigation indicated that he was a civilian worker for the Afghan police, said Mr. Graybeal, the coalition spokesman.
While Afghan recruits for the army and the police are vetted, civilian employees, especially on outlying bases, generally are not, Afghan officials said.
The Taliban's spokesman for southern and western Afghanistan, Qari Yousaf Ahmadi, said that the Taliban were not responsible for the attack.
"We don't know which kind of soldier he was, but whoever he was, he was a patriot and a hero," Mr. Ahmadi said.
Three Americans who were shot Friday at an outpost in the Sangin district of Helmand Province were members of a Special Operations unit. They were killed when they arrived at the outpost, possibly after being invited for a meal with the man who shot them.
The number of coalition service members intentionally killed this year by Afghan soldiers or police officers stands at 34 in 25 attacks -- not counting the attack on the Garmsir base because it is unclear whether an Afghan service member was responsible. In 2011, 35 were killed in 21 attacks.
Sangar Rahimi contributed reporting from Kabul, and an employee of The New York Times from Helmand Province, Afghanistan.
This article originally appeared in The New York Times.