The UK government is continuing to accuse Russian president Vladimir Putin, and his regime, of committing war crimes in Ukraine.
Preliminary international probes have already begun following Putin's brutal invasion of Ukraine.
The Office of the UN High Commissioner for Human Rights (OHCHR) says Putin's war has so far resulted in 1,626 confirmed civilian deaths and 2,267 injuries - but adds the actual figures will be "considerably higher". Meanwhile, millions of people have been displaced from their homes.
But what is a war crime, how are they prosecuted and what is the punishment? Here, Yahoo News UK explains.
What is a war crime?
There is not actually an agreed definition. As the United Nations points out, “there is no one single document in international law that codifies all war crimes”.
But the Rome Statute of the International Criminal Court (ICC), where war crimes can be prosecuted (see further information below), follows the definition set out by the 1949 Geneva Conventions, which were ratified by 196 states.
This definition includes acts of:
torture or inhuman treatment
wilfully causing great suffering or serious injury
extensive destruction and appropriation of property which is not justified by military necessity
compelling a prisoner of war to serve in the forces of a hostile state
wilfully depriving a prisoner of war of the rights of fair and regular trial
unlawful deportation or transfer or unlawful confinement
taking of hostages
However, the Rome Statute also includes an extensive list of further specific violations, such as intentionally directing attacks against civilian populations, using child soldiers, forced pregnancy and intentionally directing attacks against hospitals.
How are war crimes prosecuted?
War crimes can be prosecuted at the International Criminal Court (ICC), in The Hague in the Netherlands. This court is governed by the Rome Statute outlined above.
The ICC, which began operations in 2002, "investigates and, where warranted, tries individuals charged with the gravest crimes of concern to the international community". This includes war crimes as well as genocide, crimes against humanity and the crime of aggression.
It is a "court of last resort" and a case will only be heard there when a national court is not in a position to address it.
Watch: Kyiv mayor Vitali Klitschko attacks Putin: 'He's sick, he's an unhealthy man'
After gathering evidence and identifying a suspect, ICC prosecutors can request judges to issue arrest warrants. It relies on countries to carry out the arrest and a trial cannot begin until a suspect is detained and transferred to the court.
Twenty-seven defendants have been accused of war crimes by the ICC, with three - Ahmad Al Faqi Al Mahdi, Germain Katanga and Thomas Lubanga Dylio - convicted. A further eight are currently in ICC custody awaiting trial or appealing proceedings.
What is the punishment for war crimes?
At the trial, the prosecution "must prove beyond reasonable doubt the guilt of the accused" before three judges.
If found guilty, the judges can issue sentences of up to 30 years' imprisonment, or a life sentence "under exceptional circumstances".
Sentences are served in countries that have agreed to enforce ICC prison terms.
Verdicts are subject to appeal by the defence of the accused, as well as by the prosecution.
Has Putin committed war crimes in Ukraine?
Putin hasn't been formally accused of war crimes by the ICC, though it launched an investigation last month following referrals from 41 countries.
But Putin's bombardment of major cities such as Kyiv and Mariupol, including strikes on hospitals and civilian evacuation routes, have seen leaders around the world accuse him of having committed war crimes.
And on Friday, Boris Johnson joined international condemnation of a rocket strike on a railway station in Kramatorsk, eastern Ukraine, which is said to have killed at least 39 people with dozens wounded.
He told a press conference: "The attack at the train station in eastern Ukraine shows the depth to which Putin’s once-vaunted army has sunk.
“It is a war crime indiscriminately to attack civilians, and Russian crimes in Ukraine will not go unnoticed or unpunished.”
In a message to Russian people on Tuesday, the prime minister also said: "Your president stands accused of committing war crimes. But I cannot believe he’s acting in your name.”
In the past week, there were more accusations following the reported violent killing of civilians by Russian forces in Bucha, a town on the outskirts of Kyiv.
Amnesty International said the reports show a "wider pattern of war crimes including extrajudicial executions and torture in other occupied areas of Ukraine.
“We fear the violence suffered by civilians in Bucha at the hands of Russian soldiers is not unique."
Watch: Britain will do more to see Putin defeated in Ukraine - Wallace
Joe Biden has also repeatedly labelled Putin a war criminal, with the US president calling for him to face trial.
In his most recent statement on the probe on 10 March, ICC chief prosecutor Karim Khan said: "I note, in particular, that if attacks are intentionally directed against the civilian population: that is a crime. If attacks are intentionally directed against civilian objects: that is a crime. I strongly urge parties to the conflict to avoid the use of heavy explosive weapons in populated areas.
"There is no legal justification, there is no excuse, for attacks which are indiscriminate, or which are disproportionate in their effects on the civilian population."
Could Putin be prosecuted for alleged war crimes in Ukraine?
David Scheffer, who was the first US ambassador-at-large for war crimes under the Clinton administration, told Foreign Policy last month it's "inevitable" Putin will be indicted at the ICC.
"He is at the very top of the command chain in Russia.
"He has obviously failed as top commander to stop those crimes from being committed on a daily basis. He has the power to do it.”
However, as outlined above, hearings cannot begin until a suspect is arrested and transferred to the ICC.
And while the court could well accuse Putin of war crimes, asking Russia to arrest its all-powerful dictator is another matter altogether.