As these initiatives failed to halt the growth of the rebel movements, the Burundian military eventually decided to set up a new militia in Cibitoke Province, which was initially simply known as "the young men" (les jeunes or abajeunes). In contrast to previous self-defense groups which were either unarmed or dominated by Tutsi, the abajeunes were both armed as well as mostly Hutu. They consisted of ex-rebels and former civilian patrolmen who had proven themselves to be trustworthy. Trained, armed and supplied by the military, the abajeunes were a success. The program was thus expanded to the entire country; the abajeunes in southern Burundi soon became known as the "Guardians of the Peace". Numbering 3,000 fighters by late 1997, they were decisive in keeping the insurgents at bay. Nevertheless, the number of war casualties further increased in 1998. In 1998, Buyoya and the opposition-led Hutu parliament reached an agreement to sign a transitional constitution, and Buyoya was sworn in as president. Formal peace talks with the rebels began at Arusha on 15 June 1998. The talks proved to be extremely difficult. Tanzanian ex-President Julius Nyerere acted as chief negotiator, and attempted to use caution and patience to achieve a solution. Upon Nyerere's natural death in 1999, Nelson Mandela assumed responsibility for the peace talks. He and other heads of states in the region increased the pressure on Burundi's political leadership, pressuring them to accept a government with participation of the rebel groups. Meanwhile, the civil war continued unabated, despite the efforts of the international community to facilitate the peace process. Though 1999 saw a reduction of fighting, the war again grew in intensity during the following two years. The Burundian military conducted a major offensive between October and December 2000, attempting to clear the Tenga forest near Bujumbura of insurgents. Though killing many rebel fighters, the operation was a failure, and the Tenga forest remained an insurgent stronghold. After bitter negotiations, an agreement was finally reached which established a transitional government, where the presidency and vice-presidency would be rotated every 18 months, sharing power between the Hutus and Tutsis. While the Burundian government and three Tutsi groups signed the Arusha Accords ceasefire accord in August 2000, two leading Hutu rebel groups refused to participate, and the fighting continued. The Arusha talks closed on November 30, 2000. Twenty Tutsis and one British woman were killed on 28 December 2000, in the