WASHINGTON — A U.S. military investigation says command failures left American soldiers in an indefensible position without adequate support when hundreds of insurgents attacked their remote outpost in northeastern Afghanistan with rocket-propelled grenades, mortars and guns.

Eight U.S. troops were killed and 22 were wounded during the October 2009 attack on Combat Outpost Keating, one the deadliest battles during the nearly decade-long war. The investigation released Friday by U.S. Central Command in Tampa, Fla., recommended giving four officers letters of admonition or reprimand for putting the 53 American troops in a vulnerable position at the outpost in mountainous Nuristan province near the Pakistan border.

Documents show Stanley McChrystal, then the top American general in Afghanistan, approved the decision to punish the officers — a captain, a major, a lieutenant colonel, and a colonel. For their privacy, their names were removed from the copy of the report posted on Central Command's website. The investigation says the soldiers from B Troop, 3rd Squadron, 61st Cavalry, were in a "tactically indefensible position" with an "unclear mission."

The investigation, led by Army Gen. Guy Swan, said in the weeks before the attack there were reports of a large enemy force massing near Keating and preparing for an attack. Those reports were sent up the chain of command, "but there was an inadequate response, and ultimately, a failure of intelligence to prepare the unit for the enemy's action," according to the inquiry.

The report also says there were too few troops at Keating. And because the base was scheduled to be closed, the construction of barriers and other defenses weren't pursued "since improvements would be of limited duration," the report said.

But McChrystal, who was removed last summer as U.S. commander in Afghanistan after a magazine article anonymously quoted people around him criticizing members of President Barack Obama's national security team, praised the officers' prior performance and acknowledged the tough circumstances they faced.

In a December 2009 memo, McChrystal said he recognized the "extremely difficult missions and extraordinary responsibilities we have given these officers in a challenging, complex combat environment."

Many of the Afghan soldiers stationed alongside the American troops at Keating either ran or hid during the firefight, according to witness statements included in the investigation. The U.S. has spent billions of dollars training and equipping the Afghan army and police.

Capable Afghan security forces are an essential ingredient in the Obama administration's plans to begin withdrawing American forces from Afghanistan. But among the dozens of witness statements are withering critiques of how the Afghan troops performed during the firefight at Keating.

One witness, identified only as a first sergeant with B Troop, called the group of Afghan soldiers at Keating "horrible" and "worthless."

Another soldier who worked with the Afghan troops at Keating and Outpost Fritsche, a nearby base attacked at the same time, said the Afghan troops refused to go on patrols and sold supplies they got from the Americans to the locals.

The soldiers from B Troop weren't supposed to still be at Keating when the attack occurred on Oct. 3, 2009. The base's closing was scheduled months earlier as part of McChrystal's strategy to shutter isolated bases and have U.S. forces focus on more populated areas to protect civilians.

Keating's closure was delayed after equipment and supplies needed to move the troops and their equipment were diverted to support operations in another area.

Keating was closed three days after the attack.