Liberia's President Ellen Johnson Sirleaf, Africa's first democratically elected female leader, has easily won a second term in a run-off election boycotted by her rival.

With almost all the ballots counted from Tuesday's voting, the election commission said Mrs. Sirleaf won more than 90 percent of the vote while opposition candidate Winston Tubman took 9 percent. Voter turnout was low.

Tubman boycotted the runoff saying it was rigged in favor of President Sirleaf. He says he will refuse to accept the results.

Election observers from the U.S.-based Carter Center says the run-off was credible and met international standards for democratic elections. They reject Tubman's assertion that the election was seriously flawed.

State Department spokesman Mark Toner says the United States is disappointed the opposition boycotted the vote. He is urging all Liberians to peacefully accept the results.

Mrs. Sirleaf insisted the electoral process was legitimate and vowed to reach out to Tubman and other party leaders.

Analysts say the legitimacy of her re-election may be marred by the boycott, low voter turnout, and deadly clashes between police and opposition protesters just before the run-off. The Liberian government has also been criticized for responding to the unrest by closing three pro-opposition radio stations.