KINSHASA, Congo - Congo's opposition leader has declared himself winner of the presidential vote, despite placing second in official election results.

Etienne Tshisekedi said Sunday at a news conference that incumbent President Joseph Kabila's government "is dismissed starting today."

Sunday's declaration comes only two days after the country's supreme court upheld incumbent President Joseph Kabila's victory in the November vote.

International observers, however, have expressed concerns about irregularities, saying voter turnout was impossibly high in some districts.

Congolese government spokesman Lambert Mende said he had not comment on Tshisekedi's declaration.

Tshisekedi urged his supporters Sunday to remain calm, so as not to frighten foreign investment in the mineral-rich nation.