At the same time Mengistu was resisting reforms, Eritrean and Tigrean insurgents were placing the regime in an increasingly tenuous position. Beginning in mid-1989, Moscow began cutting back weapon deliveries and advised Mengistu to seek a negotiated settlement. In July 1989, the head of the Soviet Foreign Ministry's African Department, Yuri Yukalov, met with Eritrean representatives in London in an attempt to advance the peace process. In September 1989, the Soviet Deputy Minister of Defense, General V. Varennikov, delivered a message to Mengistu from Gorbachev confirming Moscow's decision to end military aid to Ethiopia. In early 1990, the Soviet Union sought to further its disengagement from Ethiopia by welcoming the entry of the United States into the diplomatic process. This included mediation between the regime and the Eritrea People's Liberation Front by American Assistant Secretary of State for African Affairs Herman Cohen. These talks collapsed when the Ethiopian insurgents, under the umbrella grouping known as the Ethiopian People's Revolutionary Democratic Front, overthrew the communist dictatorship in May 1991 and forced Mengistu into exile in Zimbabwe.