Russia’s decision to seal off the steel factory where Mariupol’s remaining defenders have made their last stand may mark the end of the battle for control over the port city. The propaganda war over its capture, however, has only begun.

There’s already been a ferocious contest over Twitter hashtags (including the name Mariupol) to own the narrative of the 52-plus-day siege, one initially dominated by pro-Ukrainian channels and voices, but increasingly — as Russian troops began to take over the city — challenged by Moscow’s supporters.

As the investigation of reported rapes, executions and other potential war crimes showed after Russian troops withdrew late last month from northern towns such as Bucha, near the capital Kyiv, possession of sites is all important. With its dominance in Mariupol, Russia has a freer hand in its efforts to control and present any findings on what happened there.

That’s become increasingly important for the Kremlin as only in Mariupol has there been even a notional basis to paint Russia’s invasion as — in President Vladimir Putin’s words — a “noble” effort to rescue ethnic Russians from fascism. The city is where the right wing Azov battalion, a former volunteer militia with an infamous insignia similar to the Nazi-appropriated “Wolfsangel,” has fought to the end.

Avoiding a larger repeat of the Bucha revelations — and indeed accusing Mariupol’s Ukrainian defenders of crimes — is now a critical focus for Putin’s messaging machine at home.

It’s all the more important with the approach of Moscow’s annual May 9 Victory Day parade to celebrate the Soviet Union’s defeat of Nazi Germany in World War II, where the Russian president is expected to trumpet the war’s success and necessity to people facing the economic upheaval of unprecedented sanctions from the U.S. and its allies.

The portrayal of Mariupol’s “liberation” and “denazification” has been both strongly promoted and tightly controlled within Russia, potentially contributing to an increase in public support for Putin since the invasion began, even if there are questions about the current reliability of polling.

Some of the campaign is spread by pro-Russia accounts and bots on Twitter and Telegram, often subtitling clips from state news channels to reach a wider international audience in English. At times diplomats have become involved, such as when the Russian Embassy to the U.K. posted a Tweet (later removed) to argue that casualties from the March 9 bombing of Mariupol’s Maternity Hospital No. 3 had been staged.

The Russian embassy in Singapore posts daily English language summaries of the war’s coverage by Russian media on its Facebook page. It routinely calls out alleged “fake” news reporting on Ukraine outside Russia.

A report by Mythos Labs, a group that seeks to counter harmful online narratives, found at the start of the war that the volume of Ukrainerelated Tweets from accounts that spread pro-Russian disinformation had increased by 1000% in just two weeks.

Twitter said on April 5 it had removed 100,000 accounts since the war started. It also stopped amplifying posts from governments “that limit access to free information and are engaged in armed interstate conflict.”

Russia’s arguments have been picked up by state media in countries such as China, including the accusation that Ukrainians staged executions in Bucha (since disproved by satellite imagery). But so far there is little sign the campaign has been able to undermine support for Ukraine in Europe, the U.S. or other nations that have condemned the Feb. 24 invasion.

Thursday’s decision to avoid a final battle in Mariupol may be part of Russia’s information control efforts for its own people.

Ukraine’s recent success in sinking the Moskva, the flagship of Russia’s Black Sea Fleet, was a prestige blow, according to a person close to the Defense Ministry. Avoiding major Russian casualties in an inch-by-inch battle for control of Mariupol’s sprawling Azovstal steel plant would be important, the person said, asking not to be identified talking about sensitive matters.

At the same time, Russian probes into what the Kremlin has called potential Ukrainian war crimes in Mariupol have already begun. State controlled RIA Novosti agency showed investigators photographing damage at a city hospital, where Russian fighters made claims — impossible to verify — that civilians had been shot by Ukrainian snipers.

In an April 14 report by TeleSur, the Caracas-based English language news channel co-funded by Cuba, Nicaragua and Venezuela to provide an alternative to global channels such as the BBC or CNN, a reporter toured the ruins of Mariupol’s theater, destroyed amid constant air strikes. He cited, without examination, Russia’s claim the theater was blown up from within by Ukrainian soldiers.

The report went on to follow Maxim Grigoriev, appointed by Russia as special investigator into crimes against humanity in the Donbas region, who accused the Ukrainian defenders of firing from civilian buildings and positioning artillery next to them. In 2019, he conducted a similar interview-based counter-narrative to discredit an international finding that the Russia-backed regime in Syria used chemical weapons.

Some Russian statements about Mariupol, as with Bucha, have been proved untrue. Those include the embassy claim that casualties at Maternity Hospital No. 3 were faked. Associated Press reporters in the city at the time confirmed the death of one of the two mothers photographed.

An April 13 report by the Organization for Security and Co-operation in Europe rejected Russia’s account of both the theater and maternity hospital bombings, declaring them evident war crimes. The OSCE also said that as the aggressor, Russia bears overall responsibility for the conflict.

Ukraine has warned that kind of fabrication will be conducted on an industrial scale in Mariupol. Its intelligence agency said in a post on its Telegram channel this month that Russia had moved 13 mobile crematoria to Mariupol to burn bodies. In a Thursday post, Mariupol Mayor Vadym Boychenko said a mass grave detected by private satellite image company Maxar Technologies could contain thousands of bodies. It wasn’t possible to verify either claim. Russia denies responsibility for any war crimes.

Ukraine has accused Russian forces of indiscriminately shelling cities and targeting clearly-marked civilian bomb shelters, such as Mariupol’s theater, and evacuation corridors. Some of those charges have been independently verified.

In urban warfare, residential as well as other buildings invariably are used by both sides to provide cover, but after weeks of constant Russian shelling and aerial bombardment, there’s little doubt as to what caused the vast majority of the damage in Mariupol.

Ukraine has had its own war crimes allegations to deal with, though far fewer. These include a video widely reposted on pro-Russia sites of soldiers appearing to shoot Russian prisoners of war in the legs as they interrogated them near Kharkiv, around March 26. The OSCE and Human Rights Watch found it a potential war crime. Ukraine said it would investigate.