Two American advisers , one soldier and one civilian, were killed in Afghanistan Wednesday.

Three others, one soldier and two civilians, were injured as well, in "an attack near a coalition base by an unknown assailant," the public affairs office of the U.S. Forces in Afghanistan said in a statement.

CBS and Reuters report that a gunman in an American army uniform opened fire on the Americans near a base close to Kabul. That assailant was later killed.

"Anytime we lose a member of our team, it is deeply painful," said Gen. John W. Nicholson, commander of the U.S. Forces in Afghanistan. "Our sympathies go out to the families, loved ones, and the units of those involved in this incident."

The identities have been withheld as of Wednesday morning, until next-of-kin are notified.

The slain and injured were part of the larger NATO mission to "train, advise, and assist" Afghanistan's security services.

The U.S. Forces in Afghanistan "will continue to pursue our train, advise, and assist mission to help our partners create a better Afghanistan," Nicholson noted.

The deaths come after President Obama in July announced a larger than originally planned residual force in the country -- 8,400 American troops until the end of his term. That number is still far less than the 38,000 troops stationed there when he took office -- or the 17,000 additional troops he approved for the country soon thereafter.

"The security situation in Afghanistan remains precarious," Obama said, announcing his July decision. "Even as they improve, Afghan security forces are still not as strong as they need to be… we have to deal with the realities of the world as it is."