Describing the Zimbabwean general election last week, Olusegun Obasanjo, the head of the African Union observer mission, used the word “free” readily, but the term “fair‘‘ caught in his throat. Was the voting -- based on a roll that included 1.7 million voters who are missing or dead, and featuring 35 percent more ballots than people casting them - - fair? Obasanjo shrugged, turned his hands palm up, cocked his head and uttered, ‘‘fairly.’’

The AU and the Southern African Development Community nevertheless endorsed the election, allowing Robert Mugabe, 89, the world’s longest-serving ruler, to declare victory in the presidential race, with 61 percent of the vote. His party, which had held a minority of parliamentary seats, claims to have won a two-thirds majority, enough to change the constitution on its own.

The AU and SADC teams, the only external groups Mugabe allowed to monitor the poll, were plainly relieved by the absence of violence: In the 2008 election, 200 opposition supporters were killed. Nevertheless, they should have made more of their obvious (and documented) reservations about vote-rigging.

It’s not too late. Presidential candidate Morgan Tsvangirai of the Movement for Democratic Change has vowed to submit a dossier of fraud allegations to the monitors. If the evidence stands up, they should pressure the Zimbabwe Electoral Commission to order a new election. The commission is widely regarded as under the sway of Mugabe’s party, the Zimbabwe African National Union-Patriot Front. However, the resignation of a commission member over the conduct of the election suggests Mugabe may have pushed it too far.

Most of the complaints stem from the dodginess of the voter roll. The commission released the list only two days before the election, leaving no time for voters, parties and candidates to inspect and verify it. The independent Zimbabwe Research and Advocacy Unit reported that 1.7 million of the people listed were either dead or had left the country.

Eligible voters, on the other hand, were left out in constituencies likely to support Tsvangirai and his party. The Research and Advocacy Unit calculated that almost 2 million people younger than 30 were excluded. The Zimbabwe Election Support Network, which fielded about 10 times as many observers as the AU and SADC, estimated that 1 million people in urban areas were kept off the roll. According to the network, 99.97 percent of rural voters were registered, versus 67.94 percent of urban voters; 82 percent of urban polling stations turned voters away while only 38 percent of rural stations did so. A suspiciously large proportion of those who did vote -- as high as 26 percent in some polling stations, according to the AU -- required ‘‘assistance.’’

Excluded from sending observers, the U.S. and its allies had no choice but to rely on monitoring by others. To their credit, they have chosen to look askance at the regional groups’ rubber stamp.

The U.S., U.K. and European Union, which have all imposed sanctions on Zimbabwe for earlier assaults on human rights and the rule of law, expressed concern about the election irregularities. They should go further and follow the lead of Australia, which called on Zimbabwe to conduct a new, legitimate election and said it would maintain sanctions until it does. President Barack Obama had said Zimbabwe’s election could create an opening for improved relations; he should say that chance has been squandered. The EU, which had been easing sanctions to encourage political reform, should think again.

With this vote, Zimbabwe could have ended the isolation that its authoritarian order and corrupt elections have provoked for the past decade. Instead, Mugabe calculated he could continue stealing, as long as he did so bloodlessly. He shouldn’t be allowed to get away with it.

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