Silicon Valley companies have been rewriting their rules during the war in Ukraine. Russia is retaliating.

Meanwhile, the Russian government said Friday it was blocking popular Instagram, taking further action against Meta — the parent company of Facebook, Instagram, and WhatsApp — because of reports the previous day that Facebook had allowed posts which called for the death of Russia’s leader Vladmir Putin. It had previously blocked Facebook.

The moves by the Russian government show how the Kremlin is increasingly willing to censor free expression and retaliate against tech companies in what some are calling a new digital iron curtain. But the tech companies themselves, experts said, are rewriting their rules as they go in response to the fast-moving conflict, tweaking policies and struggling to maintain a consistent stance as events evolve.

“This is clearly a crisis information environment and tech companies are making many decisions on the fly,” said Graham Brookie, senior director of the Atlantic Council’s Digital Forensic Research Lab.

The resulting Russian retaliation is further cutting people off from valuable Internet services, he added, something that could “make it harder to hold the Russian government accountable for its actions.”

Facebook pushed back against criticism that it was inconsistent and said that the extreme nature of current events required the company to be nimble in its judgment calls.

“I want to be crystal clear: Our policies are focused on protecting people’s rights to speech as an expression of self-defense in reaction to a military invasion of their country,” said Nick Clegg, the company’s president for public affairs. “The fact is, if we applied our standard content policies without any adjustments we would not be removing content from ordinary Ukrainians expressing their resistance and fury at the invading military forces, which would be rightly viewed as unacceptable.”

Russia’s top prosecutor said Friday that the government was opening a criminal case against Meta and is seeking the classification of the company as an “extremist organization and the prohibition of its activities” on Russian territory, alleging the platform was used to incite “mass riots accompanied by violence.”

The country’s media regulator also said in a news release that access to Instagram was being curtailed in the country on Friday due to posts “containing calls to commit violent acts” against Russian citizens in response to the invasion of Ukraine.

The crackdown on Instagram comes one week the government’s Internet censor announced it would block Facebook, which is far less popular in Russia. Meta said the shutdown was retaliation because the company had refused to stop fact-checking posts on state-controlled media outlets Sputnik and RT.

On Thursday, Facebook’s own content moderators leaked new guidelines which showed that Facebook had decided to break its own rules to allow for some calls to violence against Russian invaders. The company confirmed the leak.

On Friday YouTube also took stronger action against state media.

“Our community guidelines prohibit content denying, minimizing, or trivializing well-documented violent events,” YouTube tweeted. “In line with that, we are also now blocking access to YouTube channels associated with Russian state media globally, expanding from across Europe.”

But experts said that for years Silicon Valley companies have allowed Russian state-owned media services to publish twisted narratives about world events and minimize violence, including playing a role in downplaying the war in Syria.

The coronavirus pandemic is a major example, Brooke said. Tech companies for years said they would not block misinformation on their platforms because they did not want to be arbiters of truth, but then they began removing content regarding coronavirus that experts said went against public health guidelines.

Meta, Google-owned YouTube and other social media companies have faced immense pressure to isolate and crack down on Russia since the invasion of Ukraine. Facebook, TikTok and YouTube banned Russian state media in Europe and in Ukraine in response to government requests, limiting Moscow’s ability to spread misinformation to millions of people. But the Ukrainian government has pressed the companies to go further — imploring them to fully shut down their services in Russia as punishment for its aggression.

Facebook has refused, arguing its services are critical for activists and everyday Russians to communicate with their families. But last week, Russia’s Internet censor said it was blocking Facebook anyway. On Friday Instagram was added to the list.

Russia’s Investigative Committee on Friday opened a criminal case against Meta and is seeking the classification of the company as an “extremist organization and the prohibition of its activities” on Russian territory, alleging the platform was used to incite “mass riots accompanied by violence.” The consequences of such an inquiry were not immediately clear.

The move by Facebook on Thursday to allow some calls for violence against Russian forces as the assault on Ukraine rages created an unusual exception to long-standing rules that prohibit such language. The change also allows users to call for the death of Russian President Vladimir Putin or his ally, Belarusian President Alexander Lukashenko, in countries including Russia, Ukraine and Poland, the company said.

Dozens of nations have clapped sanctions on Russia, targeting the country’s economic arteries as a means of threatening Putin’s war chest. That’s left companies scrambling to reevaluate their business relationships in the country and set off a flurry of announcements: On Thursday, Goldman Sachs announced it was “winding down” its business in Russia, following hundreds of other Western firms that have closed or suspended operations. Japanese clothing retailer Uniqlo and U.S. chain Victoria’s Secret also joined the list by announcing they will temporarily close Russian stores, prompting long lines as shoppers queued for what might be their last chance for months to purchase the goods.

The U.S. already has halted imports of Russian oil and energy products, which made up about 60 percent of the $26 billion in goods American buyers imported from Russia last year. On Friday, the White House announced a ban on additional goods, including vodka, diamonds and seafood. President Biden also unveiled additional sanctions aimed at Russian executives and said the U.S. would join its allies in cutting off Russia’s access to financing from the World Bank and the International Monetary Fund.