"The outcome did not reflect the true and genuine will of the Zimbabwean people or produce a legitimate result," the statement said. Mugabe, who has ruled Zimbabwe since independence in 1980, was sworn in on Sunday barely an hour after the Election Commission declared that he won more than 85 percent of the votes cast.
Mugabe had lost the first round to opposition leader Morgan Tsvangirai, who pulled out of the run-off election citing a campaign of violence against his supporters.
Ban "encourages efforts of the two sides to negotiate a political solution that would end violence and intimidation," the statement said.
It said that the UN was "ready to help in any way possible to produce this result.