Russian forces attacked a kindergarten and an orphanage in an act of "war crimes" and in violation of the Rome Statute, Ukraine's foreign minister said Friday.

"Together with the General Prosecutor's Office we are collecting this and other facts, which we will immediately send to The Hague. Responsibility is inevitable," Foreign Minister Dmytro Kuleba said on Twitter, referring to the U.N. International Court of Justice.

Tensions started escalating late last year when Ukraine, the U.S. and its allies accused Russia of amassing tens of thousands of troops on the border with Ukraine.

They claimed Russia was preparing to invade its western neighbor, allegations consistently rejected by Moscow.

Defying threats of sanctions by the West, Moscow earlier this week officially recognized Donetsk and Luhansk as independent states, followed by the start of a military operation in Ukraine on Thursday.

Russian President Vladimir Putin said the operation aims to protect people "subjected to genocide" by Kyiv and to "demilitarize and denazify" Ukraine while calling on the Ukrainian army to lay down its arms.