Furious Russian officials have threatened “scumbag” presidential election saboteurs with eight years in prison for pouring green ink into ballot boxes.

The crackdown comes ahead of an expected “flash mob” protest at noon on Sunday, the final day of voting, at the urging of exiled opposition leaders.

The peaceful strategy was endorsed by Alexei Navalny not long before his death at the hands of Russian authorities while locked up in a gulag in Siberia.

At least two more attacks on ballot boxes were reported on Saturday, adding to roughly 15 recorded on Friday. The attacks have pressured officials into tightening security at polling stations across Russia.

Ella Pamfilova is the official face of the Kremlin’s election machine and has been fronting hour-by-hour coverage of the election with regular press conferences from the Central Election Commission’s headquarters in Moscow.

On Friday, she initially tried to waive off the attacks by claiming that voting had been smooth.

But as they grew she lost her temper and called the protesters “scumbags” who “destroyed the votes of people”.

By Saturday morning, she appeared to have regained her composure and was back to insisting that voting was proceeding well, turnout was high and a new electronic voting system was working effectively.

“We have prevented all kinds of liquid injections at 20 polling stations and eight arson attempts. In one case, they tried to use a smoke bomb,” she said.

The attacks and unrest around the election have infuriated the president, Vladimir Putin, who had wanted to showcase Russians’ support for his war in Ukraine.

He looked visibly angry at a meeting of his Security Council on Friday, blaming Ukraine for launching attacks on Russia to try to disrupt the election.

Protests are banned in Russia and Russian MPs said on Saturday that they wanted to increase the punishment for sabotaging ballot boxes to eight years in prison from five.

They accused the saboteurs of being motivated by money and said the attacks had been organised by a foreign power.

“More severe responsibility should also be borne by those who act on behalf of or in the interests of a foreign state that opposes the Russian Federation during hostilities,” said Yana Lantratova, a Russian MP.

At least two petrol bombs have been also lobbed at polling stations in Russia and several voters have set fire to their ballot papers in protest at the Kremlin’s war in Ukraine.

As well as beefing up security at polling stations, OVD-Info, a Russian human rights group, said that users of the Telegram social media app were being sent messages telling people “not to succumb to the ideas of people who want to set you up, and to vote calmly, without queues and provocations”.

But the protests continued anyway on Saturday, with a video from Kaliningrad, the Kremlin’s exclave within the EU, showing a woman being detained after pouring green ink into a ballot box.

Another video from Yekaterinburg in the Urals showed an official grappling with a woman who had tried to throw green paint at a ballot box. 

The Evening Journal, a Yekaterinburg newspaper, said that the woman was a professor at the Urals Federal University.

“At the moment, the woman is in the police department. She is facing criminal charges,” it reported.

Most of the attackers appear to be middle-aged women, a sometimes subversive sub-group of Russia’s population.

The Kremlin wants to set a record win at the election for Putin and has used its election-rigging operation to manipulate the results.

This included disqualifying any real opposition candidates in the run-up to the election. Boris Nadezhdin, one of two disqualified anti-war candidates, has said police detained his staff on Friday at polling stations.

Ukrainian attacks also continued on Saturday with reports that two oil refineries in Samara, central Russia, had been attacked by drones. Ukraine has been targeting Russian oil refineries to drive up fuel prices.

Russia’s FSB security service also said it had foiled a plot by a Ukraine-backed agent to sabotage the Trans-Siberian Railway in the Sverdlovsk region in the Ural mountains and officials in Russia’s southern region of Belgorod reported that Ukrainian shelling has killed three people.

Pro-Ukraine Russian neo-Nazi militia also said they had captured 25 Russian soldiers during raids this week, their biggest against Russia since the start of the war.