In 1992 Uzbekistan adopted a new constitution, but the main opposition party, Birlik, was banned, and a pattern of media suppression began. In 1995 a national referendum extended Karimov’s term of office from 1997 to 2000. A series of violent incidents in eastern Uzbekistan in 1998 and 1999 intensified government activity against Islamic extremist groups, other forms of opposition, and minorities. In 2000 Karimov was reelected overwhelmingly in an election whose procedures received international criticism. Later that year, Uzbekistan began laying mines along the Tajikistan border, creating a serious new regional issue and intensifying Uzbekistan’s image as a regional hegemon. Following the terrorist attacks of September 11, 2001, Uzbekistan provided logistical support to the U.S. antiterrorist campaign in Afghanistan. This move continued a rapprochement that began in the late 1990s. However, in 2004 the United States cut non-humanitarian aid to Uzbekistan, citing recurrent human rights violations. In mid-2005 brutal suppression of riots in Andijon brought severe criticism from the United States and the European Union (EU). Under pressure from the Karimov regime, the United States vacated its air base at Khanabad, and sanctions by the EU and the United States followed. In the same period, a bilateral treaty substantially enhanced relations between Russia and Uzbekistan.