The 2006 Riga summit was held in Riga, Latvia, and highlighted the issue of energy security. It was the first NATO summit to be held in a country that had been part of the Soviet Union. At the April 2008 summit in Bucharest, Romania, NATO agreed to the accession of Croatia and Albania, both of which joined NATO in April 2009. Ukraine and Georgia were also told that they could eventually become members. The issue of Georgian and Ukrainian membership in NATO prompted harsh criticism from Russia, as did NATO plans for a missile defence system. Studies for the system had begun in 2002, with negotiations centered on anti-ballistic missiles being stationed in Poland and the Czech Republic. Though NATO leaders gave assurances that the system was not targeting Russia, Russian Presidents Vladimir Putin and Dmitry Medvedev criticized the system as a threat.