(Photo Courtesy ISAF Media)

The attack is the deadliest instance of friendly fire in Afghanistan since the war began.

"The incidents of Afghans turning against their coalition partners seem to reflect growing anti-foreigner sentiment independent of the Taliban," according to the Washington Post. "Afghans are increasingly tired of the nearly decade-long war and think their lives have not improved despite billions of dollars in international aid."

The incident happened after an argument broke out between the man -- Ahmad Gul, a 48-year-old veteran of the Afghan air force -- and the U.S. military personnel training the air froce.

Gul's brother said he was under immense pressure at the time.

“He was under economic pressures and recently he sold his house. He was not in a normal frame of mind because of these pressures,” said Dr. Mohammad Hassan Sahibi, his brother. “He was going through a very difficult period of time in his life.”

While the Taliban claimed responsibility for the attack, ISAF officials say there is no indication militants were involved.

There is reason for the confusion, however.  "The attackers are sometimes actually members of the Afghan security forces, and sometimes insurgents impersonating servicemen," reports the BBC.

There have been seven such attacks in 2011 alone, according to the Washington Post.

Meanwhile, Pakistani officials have been encouraging Afghanistan to ally itself more closely with countries like China instead of the United States, and to sever all ties with the West.

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Reach Executive Producer Mary Slosson here.  Follow her on Twitter @maryslosson.