Many Ukrainians have fled their homes as Russia attacks Ukraine. One of them is an 11-year old boy who traveled 700 miles to Slovakia with a plastic bag, a passport and a telephone number written on his hand.

His mother, Yulia Pisetskaya, put her son on a train to Slovakia from Zaporizhzhia, in southeastern Ukraine. She stayed behind because she needed to look after her disabled mother, per The Guardian.

Once he crossed over the border, Slovakian customs officials and volunteers called the number on the child’s hand, reuniting him with his relatives in Bratislava, the Slovakian capital.

“Little Hassan is only 11 years old, but in his way he has shown huge determination, courage and fearlessness that sometimes adults don’t have,” Roman Mikulec, Slovakia’s interior minister, said on Facebook on Monday after a meeting with the boy, who traveled hundreds of miles by train on his own.

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The boy’s mother was relieved when she found out that he managed to survive his journey.

“I am very grateful that they saved the life of my child,” Pisetskaya said in the video message Sunday, according to a translation posted on Facebook by the Slovakian Embassy in London. “In your small country, there are people with big hearts.”

Russian troops attacked the Zaporizhzhia Power Plant, which is Europe’s biggest nuclear power plant, in the early hours of Friday.

The attack was “incredibly reckless and dangerous. And it threatened the safety of civilians across Russia, Ukraine and Europe,” said Linda Thomas-Greenfield, U.S. ambassador to the United Nations.

More than 1.7 million refugees have left Ukraine since the Russian invasion started, according to U.N. data.