Russian election officials have called for the result of a gubernatorial ballot in the country’s far east to be annulled because of widespread voter fraud, in the first decision of its kind in more than a decade.

Voters in the Primorsky Krai region looked set on Sunday to reject an incumbent governor from the ruling United Russia party, led by allies of Vladimir Putin. A groundswell of support for a Communist party challenger had followed plans to raise the pension age by five years for both men and women, delaying retirement for millions.

But in a suspicious last-minute shift a number of precincts suddenly delivered 100% of their votes to the acting governor, Andrei Tarasenko, handing him a victory that appeared moments earlier to be mathematically impossible.

The suspicious results prompted protests and a short-lived hunger strike by the challenger, Andrei Ishenko, who claimed the election had been stolen.

The extraordinary call to annul the result shows the degree to which the Kremlin, which is sensitive to public opinion and the possibility for protest, must balance supporting its political allies and assuaging public anger. While Russians still largely say they support Putin, close to half say they are also willing to protest against the loss of social benefits.

Under pressure to review the vote, Russia’s elections commissioner, Ella Pamfilova, said on Wednesday that violations at a number of polling stations by both sides meant that a rerun should be held. The final decision would rest with local election officials, who meet on Thursday.

If the results are thrown out and the election held again, it would mark the first decision of its kind in more than 15 years.

Pamfilova, a former human rights ombudsman, was installed by the Kremlin in 2016 to increase trust. More than 100,000 Russians came out to protest in Moscow in 2011 over the results from parliamentary elections marred by accusations of voter fraud.

The Kremlin on Wednesday backed Pamfilova’s remarks. Putin’s spokesman, Dmitry Peskov, said : “The legitimacy, purity, transparency, and fairness of elections is more important to [Putin] than the candidate he supports.”

Tarasenko said on Wednesday he would not run in new elections. Communist officials have said they would prefer the elections be recounted, rather than held again. New elections may be held in three months’ time.