Gen. Aoun, head of the mainly-Christian Free Patriotic Movement, declared he would not unite with the Progressive Socialist Party of Druze leader Walid Jumblat and the Future Movement, a mainly-Sunni group, led by Saad Hariri, the son of slain former Prime Minister Rafik Hariri.
"We had not reached an agreement on electoral lists ... I found out that all lists were already put in place before I even returned home," Aoun told a press conference. The former army commander, who led a liberation war against Syria in 1989, returned from 14 years in exile in Paris earlier this month.
Aoun said his party would field its own candidates, including himself, in the parliamentary election to be held May 29.
The bid to drive Syrian troops and intelligence forces from Lebanon had brought together opposition groups and politicians from all factions and sects, but divisions started to surface when preparations for the elections kicked off last month.