Russia said Monday it was extending a deadline for Twitter to remove illegal content by a month to mid-May, after the social media giant started cooperating when Russia slowed down its operations.

State telecommunications watchdog Roskomnadzor imposed slowdowns on Twitter's services in mid-March, accusing it of failing to remove content related to child pornography, drug use and calls for minors to commit suicide.

The watchdog gave Twitter a month to remove the content or face a complete blockage in Russia.

The move raised concerns among Kremlin critics who fear the clampdown on Twitter and other social media is aimed at silencing opposition voices.

Roskomnadzor said in a statement on Monday that after the slowdown Twitter had deleted nearly 2,000 posts containing illegal content and was moving more quickly to take content down.

It said the slowdown measures would remain in place until May 15 but that a decision had been taken not to completely block Twitter because the US company had "for the first time" changed the way its content moderation service worked in Russia.

The statement said Roskomnadzor officials had spoken by videolink with Sinead McSweeney, Twitter's vice president of public policy for Europe, the Middle East and the Africa region.

"Roskomnadzor will continue to cooperate with Twitter management until the social network completely deletes all banned information in the quickest possible manner," the statement said.

After the slowdown began last month, Twitter denounced Russia's attempts to "block and throttle online public conversation".

The media giant said at the time it had a "zero tolerance" policy regarding "child sexual exploitation" and did not promote suicide and self-harm.

Russia has in recent months stepped up efforts to impose more control on online platforms including Facebook, Twitter and YouTube, with President Vladimir Putin saying large tech companies have become so influential that they are "competing" with sovereign states.

Putin's opponents say the efforts aim to stifle dissent, including by blocking efforts to organise protests in support of jailed opposition politician Alexei Navalny.