KABUL -- An Afghan teenager fatally stabbed an American soldier in the neck as he played with children in eastern Afghanistan, officials said Monday, as the U.S. death toll rose sharply last month with an uptick in fighting due to warmer weather.

Last week's calculated attack shows that international troops still face myriad dangers even though they are increasingly taking a back seat in operations with Afghan forces ahead of a full withdrawal by the end of 2014.

Just one U.S. service member was killed in February -- a five-year monthly low -- but the American death toll climbed to at least 14 last month.

Overall, the number of Americans and other foreign forces killed in Afghanistan has fallen as their role shifts more toward training and advising government troops instead of fighting.

But a series of so-called insider attacks on foreign troops by Afghan forces of insurgents disguised as them has threatened to undermine the trust needed to help President Hamid Karzai's government take the lead in securing the country after more than 11 years at war.

The attack that killed Sgt. Michael Cable, 26, of Philpot, Ky., last Wednesday occurred after the soldiers had secured an area for a meeting of U.S. and Afghan officials in a province near the volatile border with Pakistan.

But one of two senior U.S. officials who confirmed that Cable had been stabbed by a young man said the assailant was not believed to have been in uniform so it was not being classified as an insider attack.

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