A pre-dawn attack by the Taliban that killed three American soldiers and six other coalition troops earlier this month is raising new questions about many of the Afghan soldiers who were supposed to be fighting shoulder-to-shoulder with them.

Officials are investigating whether the Afghan troops may have colluded with the Taliban in the brazen assault on the remote coalition outpost along the mountainous Afghanistan-Pakistan border. Their findings could complicate further the already difficult challenges U.S. trainers are having with the Afghan Army.

American officials have questioned 11 Afghan Army soldiers and one Afghan interpreter who were taken prisoner after the battle and later released. Many U.S. troops in the area suspect that the Afghan POWs may have passively helped their Taliban attackers by laying down their arms, or even actively colluded with the enemy in the attack.

Details of the battle have been sketchy, since all three Americans at Observation Post Bari Alai were killed in the fight. Of the four Latvian NATO soldiers who were also defending the post, two were killed and a third was badly wounded and evacuated to Landstuhl Army Medical Center in Germany. According to a U.S. official, the remaining Latvian soldier was “shellshocked” by the attack and has been flown back to Latvia for treatment.

Three Afghan National Army troops also were killed.

U.S. officials are declining to comment on specifics until their investigation is complete. But conversations with American troops familiar with the situation reveal that in the early morning hours of May 1, more than 100 Taliban fighters launched a coordinated uphill attack on Bari Alai, a tactically critical, fortified mountaintop outpost that overlooks the convergence of the Hel Gal, Durin, Marin, and Kunar River Valleys, as well as a bridge that spans the Kunar River.

While Taliban fighters pinned down coalition troops with machine gun fire, their comrades scaled the mountainsides and advanced on the post. Coalition troops killed 19 Taliban fighters, according to U.S. officials.

U.S. Army Staff Sgt. William D. Vile, 27, who was wounded, continued to return fire as he called on his radio for reinforcements and artillery support. He was killed by an explosion and has been posthumously recommended for the Silver Star Medal, the Army’s third highest decoration for battlefield valor.

The blast breached the perimeter of the post, and the Taliban poured inside. Sgt. James D. Pirtle, 21, and Specialist Ryan C. King, 22, were killed defending the base and were both posthumously awarded the Bronze Star Medal.

After overrunning the post, the Taliban fighters captured 11 Afghan soldiers and one Afghan interpreter and transported them into the Hel Gal Valley, where they were held captive.

In the days following, U.S., Afghan, and Latvian forces embarked on joint operations to recover the dozen POWs. On May 6, approximately 400 coalition troops made a forceful push toward the Hel Gal Valley, where the POWs were believed to be held. But the mission was halted two hours after it began when the Taliban freed all 12 POWs after coalition forces broadcast radio messages demanding their return.

When asked what kind of condition the freed Afghan troops were in, Marine Lt. Col. Ted Adams replied, “Good condition. Too good, actually,” -- a sentiment echoed by other officers, which has led many to suspect that the POWs were complicit in the enemy attack.

The 12 Afghans were questioned for six days by U.S. and Afghan officials before being returned to duty on Monday. U.S. officials are declining to comment on the conduct of the Afghan troops during the attack on Bari Alai, citing the ongoing investigation.

The incident highlights the increasing level of frustration U.S. trainers are having with the wildly inconsistent performance of their Afghan Army protégés.

Additionally, American officials are becoming increasingly concerned about more sophisticated enemy tactics and massed enemy formations as evidenced at the Bari Alai post. While most of Afghanistan remains relatively calm, the Afghanistan-Pakistan border region has seen larger and more brazen enemy operations accompanied by a marked increase in violence.

Observation Post Bari Alai is now back in Coalition control.

Wade Zirkle was embedded for Fox News with U.S. and Afghan troops in the Kunar River Valley .