The White House is expected to send Vice President Harris to Poland, a source said

Russian President Vladimir Putin is meeting with members of his Security Council on March 3rd.Russian President Vladimir Putin is meeting with members of his Security Council on March 3rd. (Kremlin Press Center / Handout / Anadolu Agency / Getty Images)

There is a strong and growing chorus of calls for the International Criminal Court to prosecute Vladimir Putin. On Wednesday, the court said it would immediately begin an active investigation into possible war crimes following Russia’s invasion of Ukraine.

The US Embassy in Kyiv said on Friday that Russia had committed a war crime by attacking a nuclear power plant in Ukraine.

“It is a war crime to attack a nuclear power plant,” the embassy said says in its official Twitter show. “Putin’s shelling of Europe’s largest nuclear power plant takes his reign of terror one step further.

The alleged use by Russia of cluster bombs and so-called vacuum bombs in dense areas with many civilians has also been described as a war crime.

“I want to be very clear that Mr Putin is a war criminal,” former Ukrainian Prime Minister Arseniy Yatsenyuk told the Foreign Affairs Council on Thursday. “He has to sit behind bars in the International Criminal Court.”

However, if justice in general is moving slowly, international justice is hardly moving. Investigations at the ICC take many years. Only a handful of sentences have been won.

Here is a very broad view of war crimes and the movement for international justice:

Note: Some of what follows is from CNN’s research library, which has gathered information about the International Criminal Court.

What is a war crime? The International Criminal Court has specific definitions of genocide, war crimes, crimes against humanity and the crime of aggression. Read about them in this guide published by the ICC.

In particular, targeting civilians, violating the Geneva Conventions, targeting specific groups of people, and others could be potentially Russian war crimes.

“One thing is for sure, deliberately targeting shelling or targeting civilian or civilian targets is a crime within the court’s jurisdiction,” ICC Attorney General Karim Khan told CNN’s Christian Amanpour on Thursday.

“And even if there is a military need, there is a clear obligation for the parties to the conflict not to use disproportionate force, to make sure that the ammunition and weapons used do not have a very wide footprint in heavy civilian areas,” Khan said.

What are cluster and vacuum bombs? The fearful use of illicit weapons designed to kill without discrimination is what people are now discussing as a very specific war crime.

A cluster bomb launches a rocket and explodes thousands of feet into the air, releasing smaller bombs that each detonate when it falls to the ground. See an illustration from The Washington Post. Amnesty International reports that a Russian cluster bomb fell on a Ukrainian preschool.

“Vacuum bombs” or thermobaric weapons suck oxygen from the surrounding air to generate a powerful explosion and a large pressure wave that can have enormous destructive effects. Russia has previously used them in Chechnya, and a CNN team spotted a Russian thermobaric missile system near the border with Ukraine late last month.

Read the full analysis here.