Three American soldiers wounded Sunday in an apparent insider attack on Camp Antonik in Afghanistan's Helmand province did not sustain life-threatening injuries, a Pentagon spokesman said. 

"The three U.S. wounded in action are doing fine, none of those injuries are life threatening," Navy Capt. Jeff Davis told reporters at the Pentagon Monday.

The soldiers were wounded when they came under attack from an Afghan soldier around noon on Sunday, according to Navy Capt. William Salvin, a spokesman for U.S. Forces Afghanistan.

Several questions remain unanswered about the incident, including the gunman's identity, the military unit he was affiliated with, and whether the incident was a mistake, as some Afghan officials have said, or an insider attack.

"It is under investigation," Davis said, but he added that the incident appeared to look like an accident.

Salvin on Monday followed up by saying the incident is under investigation, "and we are not yet at the place where we have determined motive. Beyond that, we'll let the investigators do their work, and we'll let you know what they find at the appropriate time."

Camp Antonik is a smaller U.S. compound located on the larger Camp Shorabak, an Afghan military base housing Afghan commandos and the 215th Corps along with the 505th Zone National Police. The base is adjacent to what was once Camp Bastion and Camp Leatherneck, the U.S. and British military compounds that once housed thousands of U.S. Marines and British troops during the height of the military campaign in Helmand Valley.

The threat of insider attacks is still a serious threat in Afghanistan, and "we are going to look at this very closely, we are very cognizant of the threats of insider attack, and we will look very hard at our force protection measures to account for that," Davis said.