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  (Photo: REUTERS/Shamil Zhumatov)
  Soldiers of the Army National Guard 162 Engineer Company attached with 2nd Combat Engineer Battalion of U.S. Marine Corps stay next to a Mine Resistant Ambush Protected (MRAP) armored vehicle in Afghanistan, March 6, 2010.

Two U.S. soldiers in Afghanistan were killed Thursday amid days of violent protests sparked by a Quran burning incident at a joint military base. However, it was unclear if the new deaths were related to the protests. 

Two Afghan soldiers and a literary instructor gunned down the U.S. soldiers at a joint base in Afghanistan's tumultuous southeastern province of Kandahar. According to the Pentagon, a motive for the killings was not immediately clear.

The two Afghan soldiers were killed by the International Security Assistance Force, but it remains unclear whether the literary instructor managed to escape.

Thursday's attack marks the 42nd insider attack in the country since 2007 and points to the instability within Afghanistan's domestic security forces, which NATO hopes to leave in primary control of the country when it pulls out of Afghanistan in 2014.

On Saturday, two U.S. service members were gunned down at Afghanistan's heavily guarded Interior Ministry building in the capital of Kabul during the height of the protests that exploded over the burning of the Quran, which President Barack Obama called "inadvertent." Afghan security forces have said that they believe that the gunman was an intelligence official.

"There are Taliban sympathizers in uniform inside Afghan security forces who are not in fact sent or recruited by the Taliban," an Afghan government official told Reuters news agency. "The problem will not go away. We need more time, more resources and manpower."

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The Obama administration apologized for the controversial incident but faced substantial criticism, particularly following the deaths of U.S. service members in the protests. Over 30 people were killed in the protests against the Quran burning, at least five of which were NATO soldiers.

Republican presidential candidates Rick Santorum and Newt Gingrich argued that Obama's apology suggested that the act was done deliberately, when it was in fact a mistake. Despite the criticism, Obama defended his apology on Wednesday arguing that it "calmed things down."

"We're not out of the woods yet. But my criteria in any decision I make, getting recommendations from folks who are actually on the ground, is what is going to best protect our folks and make sure that they can accomplish their mission," Obama told ABC News.