MOSCOW (Reuters) - Russian police detained more than 800 people protesting against planned increases to the pension age on Sunday, a rights group said, disrupting demonstrations against an unpopular change that has hurt President Vladimir Putin’s approval rating.

The protests, organized by jailed opposition leader Alexei Navalny and his supporters, were a challenge to the authorities who were hoping for a high turnout at regional elections also being held on Sunday, despite anger over the pension move.

Footage of the protests, which were held in more than 80 towns and cities, showed the police sometimes using force to disperse rallies, beating participants with batons and dragging them away. The authorities refused to authorize most of the meetings, declaring them illegal.

OVD-Info, a rights organization that monitors detentions, said 839 people had been detained by police on Sunday in 33 cities, including some of Navalny’s closest aides.

It said most of the detentions - 354 - had been made in St Petersburg where authorities had initially authorized a rally before reversing the decision. The interior ministry was cited by the Interfax news agency as saying police had made around 100 detentions in St Petersburg and “several” in Moscow.

The proposed pension changes, which are currently going through parliament, have shaved around 15 percentage points off Putin’s popularity rating and are the most unpopular government measure since a 2005 move to scrap Soviet-era benefits.

Navalny, barred from state TV and prevented from running against Putin for president earlier this year, hopes to tap into public anger over the reform.

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He had planned to lead Sunday’s protest in Moscow, but a court last month convicted him of breaking protest laws and jailed him for 30 days. Navalny said the move was designed to derail the protests.

In Moscow, where the authorities had rejected an application from Navalny’s supporters to protest, around 2,000 people gathered in the central Pushkin Square, the authorities and Reuters reporters estimated.

Some of them chanted “Russia will be free” and “Putin is a thief.” Riot police ordered them to disperse or face prosecution. Some of the protesters then marched through central Moscow before riot police halted them with metal barriers and sometimes rough detentions.

A Reuters reporter saw at least three people being detained.

Despite the nature of the protest, many of those who took part were young.

“I have come here to protest against the pension reform, I have to live in this country and I want to have hope for the future and a good old age,” said 22-year-old Nikolai Borodin.

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Another protester, Katya Shomnikova, 23, said: “They (the authorities) stole my future life, we will have to correct what’s been done. I want a better life for myself and my children.”

After being amended by Putin, the reforms envisage raising the retirement age for men to 65 from 60 and to 60 from 55 for women. Average life expectancy for men is 66 and for women 77.

Opinion polls put Navalny’s support in the single digits, but backers note he won almost a third of the vote in a 2013 Moscow mayoral race, and believe he could give Putin a run for his money if ever allowed to run against him on a level playing field.

Putin makes a point of never mentioning Navalny by name but has suggested he is Washington’s pick for the Russian presidency.

Navalny has likened Putin to an autocratic tsar who has clung to power for too long. The authorities have not registered his Russia of the Future Party.

Elections to select the heads of 26 of Russia’s 85 regions were also being held on Sunday, including in Moscow.