The Russian state communications regulator has begun blocking access to Telegram following a court ruling against the popular messaging app last week.

Roskomnadzor said in a statement on April 16 that it had notified Internet providers that they must "restrict access" to Telegram as a result of the April 13 ruling.

Russia's moves to block Telegram have deepened concerns that the government is seeking to close avenues for dissent as President Vladimir Putin heads into a new six-year term.

Amnesty International said in April 12 that blocking Telegram, which has been used by senior government officials as well as Kremlin critics, would be "the latest in a series of attacks on online freedom of expression" in Russia.

The April 13 court decision followed a months-long standoff between Telegram and the Federal Security Service (FSB), which demanded access to its users' messages. Telegram co-founder and CEO Pavel Durov refused, saying the request was unconstitutional.

"Privacy is not for sale, and human rights should not be compromised out of fear or greed," Durov, who left Russia in 2014, said on Telegram after the ruling.

Durov had ordered Telegram's lawyers not to attend the court hearing on April 13, calling it "a farce," and Judge Yulia Smolina issued the ruling less than 20 minutes after opening the session.

Smolina said that Telegram should be blocked immediately despite rules under which Russian court decisions normally come into effect after appeals are exhausted.