In May 1997, a visit by Sassou Nguesso to Owando, Yhombi-Opango's political stronghold, led to the outbreak of violence between his supporters and those of Yhombi-Opango. On 5 June 1997, government forces surrounded Sassou Nguesso's home in the Mpila section of Brazzaville, attempting to arrest two men, Pierre Aboya and Engobo Bonaventure, who had been implicated in the earlier violence. Fighting broke out between the government forces and Sassou Nguesso's fighters, called Cobras, and led to the outbreak of the second civil war.