BBC journalist Sarah Rainsford left Russia on Tuesday, after Moscow abruptly refused to extend her work permit in what it said was a tit-for-tat row with the United Kingdom over the treatment of foreign media. The reporter was seen saying that Russian intelligence had told her she had been designated a national security threat.

Russian authorities earlier this month told Rainsford, who is one of the British broadcaster's two English-language Moscow correspondents, to leave the country in retaliation for what it called London's "discrimination" against Russian journalists working in the U.K.

Russian authorities accused London of mistreating a Russian journalist working for the state-run TASS news agency in London. They said he was forced to leave in 2019 after his visa was not extended without explanation.

They said they had tried and failed to get the U.K. to remedy the situation before deciding to retaliate in kind.

The BBC has called the expulsion of Rainsford a "direct assault on media freedom," and the British government had without success urged Russian authorities to reconsider their decision.

Rainsford, who has said she was devastated by the move, posted pictures on Twitter on Tuesday from a Moscow airport before she boarded a flight out of the country.

In a farewell report, the BBC aired footage of Rainsford first being denied entry to Russia on Aug. 10 and being told she was being denied a visa "for life."

The report showed Rainsford explaining that Russia's Federal Security Service (FSB) security service told her that she had been designated a national security threat. She said she had later been allowed to enter Russia in order to pack up her belongings.

Her departure, a de facto expulsion, follows a crackdown before parliamentary elections in September on Russian-language media at home that authorities judge to be backed by malign foreign interests intent on stoking unrest.

"At a time when Russia is seeing enemies all around, it really feels like I've been added to the list," said Rainsford.

Russia's foreign ministry has made clear it will not allow the BBC to send her back or replace her with someone else until the U.K. gives a visa to a Russian journalist it wants to be able to work in London.

In remarks to the press in March, Russia's ambassador to the U.K. said that diplomatic ties between the two countries were "nearly dead," after a U.K. strategic review this week branded Moscow an "acute direct threat."

Andrei Kelin also criticized the U.K.'s decision to bolster its nuclear stockpile, arguing the reversal of decades of policy was a violation of various international agreements.

London has also blamed Kremlin-linked actors for orchestrating attempts to hack coronavirus research labs and of trying to interfere in its 2019 general election.

Earlier, Russian Foreign Minister Sergey Lavrov also said that relations between Moscow and London are "at a freezing point" as British authorities have pursued what Lavrov called "a tough anti-Russian course" in recent years.