BEIRUT, Lebanon, March 11 (UPI) -- Syria's fragile transition from decades of the Assad family's brutal rule has been greatly shaken with an outburst of sectarian retribution and killings, posing a serious challenge to the new leadership led by Ahmad Sharaa and raising fears of civil war, disintegration and partition. The new wave of sectarian violence broke out Thursday when pro-Assad Alawite gunmen ambushed security forces of the transitional government, attacked government institutions and