Russia on Monday threatened US media operating in the country with new legal restrictions after Kremlin-controlled broadcaster RT complained of persecution by Washington.

The Russian justice ministry sent letters to "a number of US media operating in Russia" warning them of the "unacceptability of breaching Russian law," its press service said in a statement quoted by Interfax news agency.

It said the letter was "a tit-for-tat measure in response to the persecution of Russian media in the United States."

Radio Free Europe/Radio Liberty, which is US-funded, reported it received a letter warning its activities could fall under a controversial law that forces NGOs to register as "foreign agents".

This law, passed in 2012, has not so far been used against media.

It obliges groups with so-called "political" activities and international funding to call themselves "foreign agents", a term that recalls Stalin-era repression and Cold War espionage.

The rules have seen some organisations reject much-needed funding from abroad, while others have closed down.

A government source was quoted by Russia's state news agency RIA Novosti as confirming the existence of the letters.

The source said US media received "an official letter informing them of upcoming changes in Russian legislation about the broadening of the list of NGOs that can be named 'foreign agents.'"

The source said the letters had gone out to media including the Voice of America multimedia broadcaster and Radio Free Europe/Radio Liberty and its regional websites, one of which specialises in news from Moscow-annexed Crimea.

The source stressed that "these actions concern only American media, and this is an exceptional measure in response to the possible assignment of 'foreign agent' status to RT in the US."

The warnings come after the Kremlin on Friday criticised "unprecedented pressure" on Russia's RT state-controlled broadcaster in the United States and warned of possible reciprocal action.

RT, which broadcasts in English and other languages, said last month that the US Justice Department had asked it to register as a "foreign agent."

According to RT, the channel has been given a deadline of October 17 to register under FARA, a law written in 1938 to blunt Nazi propaganda, which specifically exempts news organisations.

Source: AFP