An apparent insider attack in northern Afghanistan on Saturday left four US troops wounded, USA and Afghan officials said. It's also suspected to be a so-called "green-on-blue" attack - when Afghan troops turn on their US and North Atlantic Treaty Organisation counterparts. In March another insider attack killed three USA soldiers.
The base is the headquarters of the 209th Corps of the Afghan National Army and is located near the city of Mazar-e Sharif.
NATO's Resolute Support later tweeted that seven US servicemembers were wounded and evacuated for treatment.
A spokesman for the Taliban militant group praised the attack but did not claim responsibility. According to an April report by the Modern War Institute at America's West Point it was in 2011 that "insider attacks became the preferred war-fighting tactic of the Taliban, an organization that understood well how to apply limited resources for maximum effect".
He said one of the attackers detonated his suicide vest and two others were shot dead by police as they tried to enter the compound, which also houses the regional command for Afghanistan's eastern provinces. More than 2,000 US troops have died of both combat and noncombat causes in the country since 2001. Afghan forces battled the Taliban team throughout the day before killing the last remaining attacker.More news: Rallies Against Islamic Law Draw Counter-Protests Across US
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The latest attack comes at a time when the Pentagon is planning to send nearly 4,000 additional troops to Afghanistan, hoping to break a stalemate in the 16-year war, the Associated Press reported, citing an unidentified official.
US-led North Atlantic Treaty Organisation forces confirmed that American soldiers had been wounded in "an incident" at Camp Shaheen, without specifying a number. The soldiers were assisting operations against the Islamic State in the restive eastern province of Afghanistan.
Western officials say most insider attacks stem from personal grudges and cultural misunderstandings rather than insurgent plots.
United States soldiers of Task Force Iron, taking part in Operation Resoulte Support, manuever a howitzer into position at Bost Airfield, Afghanistan, June 10.