KABUL, Afghanistan — An Afghan police officer killed at least 10 of his fellow officers on Saturday, a day after six U.S. service members were gunned down by their Afghan partners in summer violence that has both international and Afghan forces questioning who is friend or foe.  

Attacks on foreign troops by Afghans working with the alliance are on the rise and, while cases of Afghan security forces killing within their own ranks are less frequent, together they show how battle lines have blurred in the decade-long war.

The assaults on international service members have stoked fear and mistrust of their Afghan allies, threatening to hamper the U.S.-led coalition’s ongoing work to train and professionalize Afghan policemen and soldiers. The attacks also raise questions about the quality of the Afghan forces that have started taking charge of security in many areas of the country as U.S. and NATO combat troops move to withdraw by the end of 2014.

Coalition officials say a few rogue policemen and soldiers should not taint the overall integrity of the Afghan security forces and that the attacks have not impeded plans to hand over security to Afghan forces, which will be 352,000 strong in a few months. But there is growing unease between international troops and their Afghan partners and that’s something Taliban insurgents are happy to exploit.

Shakila Hakimi, a member of the Nimroz provincial council, said the policeman who opened fire on his colleagues at a checkpoint in Dilaram district is believed to have had ties to militants. He was killed in an ensuing gunbattle, she said in a telephone call from the provincial capital of Zaranj, along Afghanistan’s western border with Iran.

“The checkpoint is in a remote area of a remote district,” Hakimi said. “The telecommunications are poor and we are not able to get more details.”

Hakimi said the provincial governor has sent a team to the scene to get more details about what happened.

A day earlier, two Afghans shot and killed six American service members Friday in neighboring Helmand province in the south where insurgents have wielded their greatest influence.

In the first attack, an Afghan police officer shot and killed three Marines after sharing a pre-dawn meal with them in the volatile Sangin district, according to Afghan officials.

Sangin’s district chief and the Taliban both identified the gunman as Asadullah, a member of the Afghan National Police who was helping the Marines train the Afghan Local Police, a village-level defense force overseen by the Ministry of Interior. The district chief, Mohammad Sharif, said the shooting happened at a police checkpoint after a joint meal and a security meeting. The meal took place before dawn because of Ramadan, the Muslim holy month of fasting in which Muslims abstain from food and drink during daylight hours.

A U.S. defense official had a differing account. He said he’s read reports saying a man clad in an Afghan security forces uniform shot the Marines shortly after 1 a.m. not at a checkpoint, but on a coalition outpost. The official spoke on condition of anonymity because the incident is still being investigated.

Sidiq Sidiqi, a spokesman for the Afghan Ministry of Interior, told reporters on Saturday that the shooter may have been a member of the Afghan Local Police, but that Afghan investigators also were still reviewing the case.

Then at around 9 p.m. Friday in the Garmser district farther south, an Afghan working on an installation shared by coalition and Afghan forces shot and killed three other international troops, said Maj. Lori Hodge, a spokesman for the coalition in Kabul. A U.S. defense official confirmed the three victims also were Americans. Hodge said both shooters had been detained.

There also were differing accounts of the Garmser shooter’s identity.

The U.S. defense official said the gunman was described as an employee of the Afghan Uniformed Police. Sidiqi said initial reports were that the shooter was a student not associated with the Afghan police. Taliban spokesman Qari Yousef Ahmadi claimed the gunman was a member of the Afghan security forces.

Attacks where Afghan security forces or insurgents disguised in their uniforms kill foreign troops have spiked with four such attacks in the past week. There have been 26 such attacks so far this year, resulting in 34 deaths, according to the U.S.-led coalition. It’s unclear if the Garmser killings will be counted as one of the so-called “green-on-blue” attacks.

The Taliban claimed responsibility for both attacks in Helmand — the site of many “green-on-blue” killings.

Since 2009, 18 international soldiers, including 14 from Britain, have been killed in such attacks in Helmand. The most recent was on July 1 when three British service members were killed in Sangin by a gunman wearing an Afghan National Civil Order Police uniform.

Afghan President Hamid Karzai condemned the latest killings, ordered investigations into the incidents and directed relevant Afghan authorities to work to ensure the safety within training and security institutions.

“The enemy who does not want to see Afghanistan have a strong security force, targets military trainers,” Karzai said in a statement.