Update 1: “Several helicopters landed in and departed from the HQ compound taking out casualties. We dont know how many killed or wounded” CONFIRMED 1st-hand account

Update 2: At least 2 Americans killed, six wounded. Could be as many 9 more casualties with Afghan partner force. CONFIRMED - multiple sources

Update 3: At least 2 Americans killed while engaged by direct fire during a joint operation in Nangarhar CONFIRMED

Update 4: Deadly Attack carried out using DShk Heavy Machine Gun (also AA at close range) . 6 Severely injured + 8 ANSF SOF Members killed , 1 injured. The DShK Operator may be infiltrator. This Happened during meeting with Local Elders. Partially CONFIRMED - specific details unconfirmed

Update 5: Reports that it was perpetrated by insider and attack occurred during the night. Many believe it to be carried out by Taliban network. CONFIRMED

Update 6: Key member of Pakistani Taliban believed to be killed no name yet, unconfirmed status of individual

Update 7: Both U.S. and Afghan forces were attacked by "Direct Fire" CONFIRMED

Update 8: Taliban has claimed responsibility and says they killed "5 or 6 U.S. soldiers and 5 Afghan Troops False Claim

Update 9: NYT reports Afghan officials told them "at least 5 or 6 U.S. soldiers killed" False Claim

Update 10: USFOR-A Spokesman Col. Sonny Leggett confirms 2 US service members killed & 6 others wounded in a firefight on Feb. 8 in Nangarhar province Afghanistan after person in Afghan uniform fired machine gun @ them after “key-leader engagement”. Wounded receiving medical care at US Facility. CONFIRMED

Update 11 (Likely my final update for a few hours - updates in my absence are welcome):

• An Afghan defense ministry official, who was not identified because he was not authorized to speak to the media, said the shooter was an Afghan soldier who had argued with the U.S. forces before opening fire. He was not a Taliban infiltrator, the official said.

• In a statement, the U.S. military said “an individual in an Afghan uniform opened fire on the combined U.S. and Afghan force with a machine gun. We are still collecting information and the cause or motive behind the attack is unknown at this time.”

Additional and/or Notable Information:

• 2 US service members killed & 6 others wounded; 8 ANSOF killed
• 17 overall casualties, all evacuated to hospitals.
• 7th Special Forces Group ODA ambushed in Sherzad, Afghanistan
• Suspected Green on Blue from ANA
• DShk Heavy Machine Gun (also AA at close range) was used during attack, according to various reports. I've yet to obtain clear confirmation by US Intelligence or appropriate high-ranking official government agencies or individuals that the specific weapon-type described above is factual, however I believe there to be a high level of confidence that a rapid, automatic, machine-gun type weapon of similar description was used. You should especially take details surrounding this with a "grain of salt" until credible confirmations are provided by appropriate government sources.
• Joint operation (U.S, soldiers & Afghan security forces) taking place at time of attack involved 'key-leader' (specifics for what the involvement was aren't quite understood)
• Ambush took place during a Key Leader Engagement
• "An Afghan commando opened fire," a local security official told AFP, adding that the shooting lasted a long time.
• In the past, US forces have been targeted in so called "insider" attacks where Afghan security forces target international soldiers with whom they are working.

Clarification regarding the "insider": Official and various public reports I've read have described the attacker(s) / terrorist(s) wearing an "Afghan uniform". I've yet to confirm additional specifics regarding the attacker(s), but insider accounts have described the event using key words such as: "shocking", "surprising", "ambush", etc. A joint operation (US and Afghan forces) was underway when the attack took place, so the description of the perpetrator(s) in an "Afghan uniform" and the words used to describe the state-of-mind of those involved, both describe an attack either accurately or loosely related to one that would be perpetrated by individual(s) on the "inside". Hopefully that clears up some confusion I know many were wanting clarity regarding.