US president Joe Biden says Vladimir Putin is a “war criminal” and that information should be gathered for “a war crimes trial.”

Moscow has previously said that such comments are “unacceptable and unforgivable rhetoric.”

Here’s what the laws of war say – and some of the ways in which Russia is accused of breaking them.

And be aware: this article contains graphic descriptions and links to articles containing images that some readers may find distressing.

Killings

Russia has caused hundreds of civilian deaths since this war began. In order to consider these war crimes, we’d need proof that Putin’s forces had meant to target them.

But even if it’s not deliberate, killing civilians can break international law in other ways. Both sides have to make sure that any strikes are not indiscriminate – which means armies can’t just open fire on civilian areas.

The maternity hospital

Putin’s forces bombed a maternity hospital in Mariupol on 10 March, killing three people.

The Russian foreign minister Sergei Lavrov said that: “All expectant mothers, all nurses and other personnel had been driven out” of the facility by the far-right Azov battalion of the Ukrainian army, which Mr Lavrov claimed had turned it into their base.

Had that been true, it could have made the hospital a legitimate military target, and helped exonerate Russia from a possible war crimes charge.

Apparently trying to support this assertion, Russian authorities accused women in the graphic photos and videos that emerged from the scene of being actors.

But these claims have been debunked. We have plenty of evidence from reputable news outlets – including the Associated Press, the BBC and Sky News – that the attack and those pictured as injured in it are genuine.

The theatre

A week later, a theatre that was being used as a shelter in Mariupol was hit by an airstrike. The Ukrainian authorities blamed Russian forces, but the Kremlin claimed the bombing was carried out by Azov fighters. An estimated 300 civilians were killed in the attack, according to the local city council.

Bucha ‘genocide’

Earlier this month, pictures emerged from the city of Bucha – which was until recently under Russian occupation – that seem to show civilians having been shot and left in the streets.

Ukraine’s president Volodymyr Zelenskyy says the evidence emerging from the city points to a “genocide” of Ukrainians by Russian troops. Sergei Lavrov said claims of civilian killings in Bucha were “stage-managed anti-Russian provocation.”

Executions

There are also reports of Russian soldiers carrying out “summary executions” – when a person is accused of a crime and immediately killed without a fair trial. If these reports are proven, they could amount to war crimes.

The charity Human Rights Watch says “Russian forces in the village of Staryi Bykiv, in Chernihiv region, rounded up at least six men […] and later executed them” on 27 February. The organisation also reports that “Russian forces in Bucha, about 30 kilometers northwest of Kyiv, rounded up five men and summarily executed one of them” on 4 March.

Rape

Rape is illegal at any time, but it can also be a war crime if it takes place as part of an armed conflict. In 2008, the United Nations passed a resolution recognising the fact that sexual violence can be used as a weapon of war “to humiliate, dominate, instil fear in, disperse and/or forcibly relocate civilian members of a community or ethnic group”.

The Times spoke to a woman living near Kyiv who said that on 9 March, “Russian soldiers […] invaded [her and her family’s] home, stole from them and shot dead her husband before raping her repeatedly over the course of several hours.”

Human Rights Watch says that it spoke to another woman who told them that on 13 March, “a Russian soldier had repeatedly raped her in a school in the Kharkiv region where she and her family had been sheltering […] She said that he beat her and cut her face, neck, and hair with a knife.”

The Ukrainian MP Lesia Vasylenko claims that girls as young as ten have suffered horrific injuries after being raped by Russian soldiers. She also shared a photograph of a woman who was allegedly raped, killed and branded with a swastika.

Illegal weapons and tactics

Siege of Mariupol

A siege is when forces control the ways in and out of a city or town to trap people inside. Siege tactics can constitute a war crime if forces are bombing civilian targets inside the city – or if they block food, water or essential supplies from the people there.

President Zelenskyy and the United States have accused Russia of doing this in Mariupol. One woman who escaped the city told the BBC that children there were dying of dehydration.

Responding to these reports, Moscow claims that it is “neo-Nazis” who have held people there as “hostages”, not Russian forces. On 20 March, a Kremlin official said Russia would set up humanitarian corridors to allow “nationalists” to leave the city.

But Russia has repeatedly broken promises of a ceasefire along the routes that had been earmarked to bring aid to Mariupol residents. The International Committee of the Red Cross says thousands of civilian lives depend on these supplies reaching the city.

Banned weapons

Russia is also accused of deploying weapons that are so destructive that they can’t discriminate between civilian and military targets – making their use illegal under international law. NATO officials said last month that Russia had used one such weapon – cluster bombs – as part of the invasion. The Ukrainian authorities and the British government have also claimed that Moscow admits to using a banned vacuum bomb (sometimes known as a thermobaric weapon).

Forced displacement

Taking civilians from their own country and moving them to another is a war crime, according to the laws of war.

The Ukrainian authorities say that Putin has forcibly deported 40,000 of their citizens to Russia since the war began. It’s not clear how many are civilians, but the officials say that “many children” have been taken.

Dmitry Peskov, Putin’s chief spokesperson, says “such reports are lies.”

What happens next?

The allegations we’ve looked at here are, for now, just that: allegations. The International Criminal Court (ICC) has opened an investigation, which may end up including some of the incidents we’ve described above, and may include others we’ve yet to hear about.

But the Court has its work cut out: even if it’s able to prove that war crimes or other violations of international law have been committed, it might struggle to bring any of the accused perpetrators to justice. That’s because Russia has not signed up to the jurisdiction of the Court, and so a successful prosecution would likely rely on Moscow’s cooperation. We just don’t know if that will happen.

It’s also unclear who would stand trial if charges were brought. Philippe Sands, professor of law at University College London, told the Associated Press: “There’s a real risk you end up with trials of mid-level people in three years and the main people responsible for this horror – Putin, Lavrov, the minister of defence, the intelligence folks, the military folks and the financiers who are supporting it – will get off the hook.”

And some analysts warn that even if Putin himself were indicted, the process would likely take many years. One previous head of state to face prosecution – the Yugoslavian president Slobodan Milošević – died before his four-year-long trial had completed.