 However the guerillas were unable to fully defeat the Afghan Army as expected by the United States and Pakistan, and neither could the Najibullah government win on the battlefield.This situation ended following the 1991 August Coup in the Soviet Union - according to Russian publicist Andrey Karaulov, the main trigger for Najibullah losing power was Russia's refusal to sell oil products to Afghanistan in 1992 for political reasons (the new Boris Yeltsin government did not want to support the former communists), which effectively triggered an embargo.The defection of General Abdul Rashid Dostam and his Uzbek militia, in March 1992, further undermined Najibullah's control of the state.