A Russian court says it will begin considering this week a request by state media regulator Roskomnadzor to block the messaging app Telegram.

Moscow's Taganka district court said it scheduled the hearing for April 13, rejecting a request by Telegram to postpone it.

Roskomnadzor has asked the court to block Telegram following the company's refusal to give the Federal Security Service (FSB) access to users' messaging data.

On March 20, the regulator ordered Telegram to provide the FSB with encryption keys needed to read users' messaging data within 15 days, after the Supreme Court rejected Telegram's challenge to the demand.

Telegram has been defiant throughout the showdown. Shortly after Roskomnadzor announced it had filed suit with the Moscow district court on April 6, Telegram lawyer Ramil Akhmetgaliyev said that the company did not plan to follow the order, dismissing the FSB's demand as "unconstitutional" and "not based on law."

Ahead of the hearing, Amnesty International called the attempt to block Telegram the "latest in a series of attacks on online freedom of expression" by Russian authorities.

"In recent years the Russian authorities have steadily targeted the country's few remaining spaces for freedom of expression," the London-based rights watchdog's deputy director for Eastern Europe and Central Asia, Denis Krivosheyev, said in a statement.

"They have blocked news sites that criticize them, imposed draconian data-storage rules, and declared media outlets registered outside Russia as 'foreign agents'," he added.

Krivosheyev said Telegram, one of the most popular messaging apps in Russia, was being targeted "simply for having the courage and integrity to respect the privacy of its users."

Kremlin critics have used social media to spread the word about antigovernment demonstrations and to publicize corruption allegations against Putin, a former FSB chief and Soviet KGB officer, and his allies.