Washington (AFP) – The US balancing act in providing substantial military aid to Kiev without provoking nuclear-armed Moscow into a dangerous reaction has grown far more difficult as allegations mount of abuses and atrocities by Russian troops. Since the Russian invasion on February 24, the United States has provided Ukraine with a flood of light arms, like the shoulder-fired Javelin anti-tank missiles that have become a symbol of Ukrainian resistance. But it has also refused to provide heavy weaponry like combat aircraft which could be seen as escalating the conflict and increasing the risk o…