Democratic Republic of Congo President Joseph Kabila has been sworn in for a new term, as opposition leader Etienne Tshisekedi continues to assert he is the country's rightful leader.

Mr. Kabila took the oath Tuesday in Kinshasa, following an election last month that international observers say had many irregularities during the voting and counting process.

Mr. Kabila has said there is no question about the legitimacy of his re-election, and election officials say he easily won.

But Tshisekedi has rejected the results as fraudulent and declared himself president, saying he will take office Friday.

The United States called the vote “seriously flawed.”

Mr. Kabila has suggested Tshisekedi use the appeals system to challenge the results.

The presidential and legislative polls were only the second free elections in Congo since it was torn apart by several years of warfare that ended in 2003.