Moscow (AFP) - Russian photographer Alexander Rumyantsev never thought he was meddling in politics when he staged an art festival with funding from the US government -- but the authorities in his country decided differently.

Late last month Russia's justice ministry included the photography club Rumyantsev runs in the Siberian city of Omsk on a black list of so-called "foreign agents" -- making it one of the latest victims of a controversial law critics say is aimed at muzzling independent civil society.

"We organised a festival of photos, videos and sculpture with a grant from the American consulate," Rumyantsev told AFP of the event in the regional city of Yekaterinburg

"The event was considered political activity. It doesn't make sense to oppose it so I'm closing the club down."

Passed in 2012, the "foreign agent" legislation forces non-governmental groups that receive funding from abroad to use the charged tag -- reminiscent of the Soviet crackdown on dissidents -- if they are accused of being involved in politics.

Now, some 100 groups -- ranging from some of Russia's leading rights groups to small regional organisations -- have been caught up in the clampdown.

- 'Demonise, marginalise, weaken' -

Proponents claim the legislation -- introduced after President Vladimir Putin was elected to a third term amid popular protests -- is needed to stop Western plots to destabilise the country.

But rights activists say the authorities under former KGB agent Putin are whipping up fear in a bid to crush any voices they does not control and further cement his grip on power.

"Independent organisations across the board have been targeted - rights groups, environmentalist groups, think tanks," Tanya Lokshina from Human Rights Watch told AFP.

"It is clear that the law's being used to demonise, marginalise, weaken, and eventually destroy independent critics of the government."

Another organisation that has faced official wrath is Friends of the Siberian Forests -- an environmental group from Krasnoyarsk, in Russia's vast taiga.

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The group -- which has received financial aid from two US foundations -- has been battling against illegal logging and devastating forest fires since 1999 -- but now it could be shut down after being tagged a "foreign agent" last month.

"We don't have the money to pay the heavy fines" that authorities hit the group with when it was added to the black list, activist Anna Laletina told AFP.

In a vague explanation of its actions the Russian justice ministry's list says that both the photography club and the environmentalists had "a political objective" that was aimed at influencing "decision-making institutions to change the policy of the state."

The ministry's press service suggested to AFP that the measure was preventive and that the groups "were planning to engage in political activity by shaping public opinion."

"It seems that federal and local officials were given direct orders to go after independent groups with foreign funding," said Lokshina from Human Rights Watch.

"Russian NGOs branded 'foreign agents'... are by no means involved in 'politics'. But they're critical of the government and advocate for improvement of flawed governmental policies."

- DiCaprio denied -

The foreign agent legislation forces groups on the list to include the label on material they publish and submit to strict official checks.

While it does not oblige organisations to close down it can see them hit by fines if they do not comply. Some groops choose to reject foreign funding in a bid to get themselves taken off the list.

In September an environmental group in Russia's Far East said it was returning a grant of $159,000 from Hollywood star Leonardo DiCaprio to help protect salmon habitats.

For Russia's leading human rights organisation Memorial -- which is also listed as a "foreign agent" -- the intention behind the legislation is clear.

"Foreign agent in Russia means spy," said Yan Rachinsky, an official at the organisation, which also works to keep alive the memory of victims of Stalin-era repression.

"The objective of the authorities is to discredit NGOs and liquidate all those who defend the individual against the state."