Ukraine’s Foreign Ministry said today that Mongolia’s failure to arrest visiting Kremlin leader Vladimir Putin, wanted on an international warrant, dealt a severe blow to the international criminal law system.

Putin arrived in Mongolia today for talks likely to focus on a new gas pipeline connecting Russia and China.

An International Criminal Court arrest warrant issued last year against Putin obliges the court’s 124 member states, including Mongolia, to arrest the Russian president and transfer him to The Hague for trial if he sets foot on their territory.

Ukrainian Foreign Ministry spokesperson Heorhiy Tykhyi said Mongolia’s failure to detain Putin was “a heavy blow to the International Criminal Court and the system of criminal law.

“Mongolia has allowed an accused criminal to evade justice, thereby sharing responsibility for the war crimes,” he wrote on the Telegram messaging app. Ukraine, he said, would work with its allies to ensure Mongolia felt the consequences.

Ukraine urged Mongolia last week to arrest Putin during his visit.

Kremlin spokesman Dmitry Peskov said Moscow had no worries about any action in connection with the warrant, saying Russia had “a great dialogue” with Mongolia and all aspects of the visit had been discussed in advance.

The ICC warrant accuses Putin of illegally deporting hundreds of children from Ukraine. The Kremlin has dismissed the accusation, saying it is politically motivated.