The International Criminal Court in The Hague will join the investigation into allegations of war crimes committed in Ukraine as Russia’s destructive invasion of its resolute neighbor stretched into a third month.

A Joint Investigative Team was set up by Lithuania, Poland and Ukraine to prepare possible prosecutions within countries and before the international court. ICC Prosecutor Karim Khan and the prosecutors general of the three countries signed an agreement Monday.

The agreement sends a “clear message that all efforts will be undertaken to effectively gather evidence on core international crimes committed in Ukraine and bring those responsible to justice,” the European Union Agency for Criminal Justice Cooperation said in a statement.

Ukraine authorities have accused Russian leadership and the military of targeting civilians, claiming mass graves have been found with hundreds of victims. Russia has denied the allegations, accusing the Ukraine military of faking photos of the dead or of committing the murders and blaming Russia in a bid to strengthen international support.

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From Potemkin to Putin: What a centuries-old myth reveals about Russia’s war against Ukraine

Latest developments:

►Ukraine President Volodymyr Zelenskyy, in a tweet Sunday, thanked President Joe Biden for his leadership and support of the Ukrainian people, saying the friendship and partnership between the two countries are “stronger than ever.”

►Russia is planning a staged referendum in Kherson, a southern city that fell to Russian forces early in the war, aimed at justifying its occupation, the U.K. Ministry of Defense said. 

►Reporters who accompanied Defense Secretary Lloyd Austin and Secretary of State Antony Blinken to Poland were barred by Pentagon and State Department officials from reporting the Kyiv visit until the two men physically left Ukraine. U.S. officials cited security concerns.

►Ukrainian President Volodymyr Zelenskyy said new evidence is emerging that shows Russian troops killed tens of thousands of civilians in Mariupol and then tried to cover it up.

A resident leaves the remnants of her multi-generational home after searching for salvageable items on April 25, 2022, in Gostomel, Ukraine.

Top US officials meet with Zelenskyy, pledge more aid

Biden administration upped its financial pledge and nominated a new ambassador for Ukraine following a quasi-clandestine meeting in Kyiv between two top U.S. Cabinet officials and President Volodymyr Zelenskyy. The announcements came hours after Secretary of State Antony Blinken and Defense Secretary Lloyd Austin provided the highest-level visit to Kyiv by an American delegation since the start of Russia’s invasion.

Ukraine has repeatedly pressed the West for more powerful weapons against Russia’s campaign in the Donbas region of eastern Ukraine, where Moscow’s forces are laboring to dislodge the last Ukrainian troops in the battered port city of Mariupol.

Blinken and Austin told Zelenskyy and his advisers that the United States would provide an additional $300 million in foreign military financing and had approved a $165 million sale of ammunition. Blinken said American diplomats who left Ukraine before the war would start returning to the country as soon as this week.