Moscow (AFP) - A controversial law that would allow Russia to cut internet traffic from international servers came into force Friday, prompting fears from rights activists of online isolation.

The law, which President Vladimir Putin signed in May, requires Russian internet providers to install technical devices provided by the authorities to enable centralised control of traffic.

They will also filter content to prevent access to banned websites.

Supporters of the legislation say the aim is to ensure Russian sites keep working if they are unable to connect to international servers or in the case of a threat from abroad such as cyber attacks.

But rights activists say it is another censorship bid following previous efforts in Russia to block services such as the LinkedIn social media site and the Telegram messenger service.

Human Rights Watch warned that the law means the "Russian government will gain even greater control over freedom of speech and information online".

- 'Directly censor content' -

The internet is the country's main forum for political debate and opposing voices as well as coordinating opposition demonstrations.

"Now the government can directly censor content or even turn Russia's internet into a closed system without telling the public what they are doing or why," said HRW's deputy Europe and Central Asian editor Rachel Denber.

The bill prompted thousands of people to join street protests in Moscow and other cities in March, with some comparing it to China's Great Firewall, which heavily restricts internet access.

The Kremlin has insisted it has no desire to isolate Russian internet users.

"No one is suggesting cutting the internet," spokesman Dmitry Peskov has said, accusing protesters of suffering from "delusions."

The bill's authors say the aim is to protect the country's websites from external threats and ensure the functioning of the internet is "safe and stable."

In the event of "threats to the stability, security and integrity" of the internet in Russia, the authorities can establish centralised control by the state telecommunications watchdog.

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Internet providers have to take part in annual drills to test the technical devices needed for this.

These devices have not yet been installed by internet providers, however, and are currently being tested, the RBK business daily reported.

One of the law's authors, nationalist lawmaker Andrei Lugovoi, is a key suspect in the 2006 murder of Kremlin critic Alexander Litvinenko in Britain.