Photo from Ukraine's Defense Ministry

Ukrainian President Petro Poroshenko has thanked the Spanish authorities for an investigation into Spanish citizens' participation in the Donbas war on the side of the Russian-led forces.

"I would like to thank the Spanish government for its cooperation in this matter," Poroshenko said in an interview with the Spanish newspaper El País, the Ukrainian presidential press service said.

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According to Poroshenko, he discussed this issue at a meeting with newly appointed Prime Minister of Spain Pedro Sánchez.

The Ukrainian president particularly noted the arrest by the Spanish authorities of eight Spaniards in 2015 upon their return from Donbas where they fought against Ukraine.

"Those ultranationalists came in Ukraine illegally to kill innocent Ukrainians. This is unacceptable, this is a crime. Russia sends snipers who kill Ukrainians – both military and civilians every day. It does not matter that those criminals have a Spanish passport. They remain criminals. I am very pleased with how the Spanish authorities have investigated this case," Poroshenko said.