By Ismail Sameem

KANDAHAR (Reuters) - An elite Afghan soldier shot dead an American mentor and his translator at a U.S. base, Afghan officials said on Friday, in the first rogue shooting blamed on the country's new and closely vetted special forces.

The soldier opened fire at an American military base on Wednesday in Shah Wali Kot district, in volatile Kandahar province, said General Abdul Hamid, the commander of Afghan army forces in the Taliban's southern heartland.

"The shooting took place after a verbal conflict where the Afghan special forces soldier opened fire and killed an American special forces member and his translator," Hamid told Reuters.

At least 16 western soldiers have been killed this year in so-called green on blue shootings, which are an increasing worry for both NATO and Afghan commanders, eroding trust on both sides as Western combat troops look to leave the country in 2014.

The latest shooting will be of grave concern to both sides, at it is the first involving a member of Afghanistan's new special forces, which undergo rigorous vetting as part of their selection into the country's top anti-insurgent force.

NATO's top general in the country, U.S. Marine General John Allen, and Afghan Defence Minister General Abdul Rahim Wardak only this month signed an agreement for Afghan special troops to spearhead controversial night raids on Afghan homes, which are seen as one of the most potent anti-insurgent tactics.

Qari Yousef Ahmadi, a spokesman for the Afghan Taliban, claimed responsibility for the attack in a phone text message sent to journalists, saying the Afghan soldier was "an insurgent infiltrator called Zakerullah".

The claim could not immediately be corroborated, and the Taliban frequently claim responsibility for attacks by disgruntled Afghan soldiers. Continued...