Russia's interior ministry has offered up to 3.9m roubles (£65,000) for research on identifying the users of the anonymous browsing network Tor, raising questions of online freedom amid a broader crackdown on the Russian internet.

The interior ministry's special technology and communications group published a tender earlier this month on the government procurement website offering the sum for "research work, Tor cipher".

Before changes to the tender were published on Friday, numerous news outlets reported that it originally sought "research work on the possibility to obtain technical information about users (user equipment) of the anonymous network Tor".

According to Andrei Soldatov, an expert on surveillance and security services, the interior ministry might be exploring possible ways to restrict Tor. But the fact that the tender was publicly announced meant that those seeking greater government control of the internet had defined their next target and were sending "yet another signal" to the online community, he argued.

"It's not important if the Russian government is able to block Tor or not," Soldatov said. "The importance is that they're sending signals that they are watching this. People will start to be more cautious."

The interior ministry refused to comment on Friday afternoon.

Originally developed by the US Naval Research Laboratory as an "onion routing project", Tor is a network of virtual tunnels that allows users to hide the source and destination of their internet browsing and keeps websites from tracking them. It is often used by whistleblowers and residents of countries where the authorities restrict access to the internet, but has also been known to be used for criminal activity. A famous example was the Tor-based online market Silk Road, which was known as an "eBay for drugs" before the FBI shut it down in 2013.

Although many news outlets reported on the recent tender as a reward for "cracking Tor", internet security experts doubted Tor could be successfully decrypted, let alone for a mere 3.9m roubles.

Of all countries, the fifth largest contingent of Tor users come from Russia, where the network's popularity more than doubled in June, going from about 80,000 directly connecting users to more than 210,000. The growth followed a "bloggers law" – signed by the president, Vladimir Putin, in May – requiring any site with more than 3,000 visitors daily to register with the government. Media experts argued that the legislation would stifle opposition voices and restrict government criticism on the internet.

The move was part of a wider campaign to regulate the internet which saw the authorities block three major opposition news sites as well as the blog of anti-corruption crusader Alexei Navalny in March. Users located in Russia can now only access the news sites through anonymising services such as Tor.

This week, Putin signed a law requiring internet companies to store Russian user data in-country, where intelligence services enjoy sweeping access to electronic information through telecoms companies. Critics worry that websites such as Facebook and Twitter, which the opposition used to organise a string of huge rallies in 2011-2013, would be forced to stop operating in Russia when it comes into effect in 2016.

Unlike the Chinese system of internet censorship, which directly blocks websites such as Google, the Russian one is built on intimidation so that users "themselves become more cautious, and internet companies think up ways to block certain sites," Soldatov said.

But blogger, journalist and web entrepreneur Anton Nosik doubted that the Tor research tender would have any effect, arguing that the interior ministry was not a serious player among the various government agencies surveilling the internet but was now "trying to make a name for itself".

"The only significance [of the tender] is the money being paid and the PR surrounding it, showing that the ministry of interior is seriously working on issues of anonymising technology, so that everybody's talking about it. And everybody is talking about it," Nosik said.

More worrying, Nosik said, was leading communications provider Rostelecom's investment in Deep Packet Inspection technology that would filter web traffic based on its content rather than its source. This would severely reduce users' anonymity on the web, although Tor should be able to somewhat limit DPI capabilities, Nosik said.