Congo's veteran opposition chief Etienne Tshisekedi on Sunday called for elections to be held this year and for President Joseph Kabila to step down as scheduled on December 20.

Tensions have been growing in the mineral-rich but troubled state over fears that Kabila, in power since 2001, may try to extend his rule with a third term, beyond the constitutional maximum of two. 

Speaking at a rally in Kinshasa, Tshisekedi warned him not to try, saying it would be "high treason" if the electoral process were not launched on schedule in September.