The Senedd member says a family member has been lost, as he warns of a “new fascism in Europe”.
Ukrainian-born Welsh politician Mick Antoniw has disclosed that a relative has died in the war against Russia.
The Labour MS for Pontypridd spoke about the loss before attending a pro-Ukraine rally in Cardiff.
He has just returned from delivering aid to the country, and said its people were continually hearing about “atrocities, torture, concentration camps, liquidation squads”.
“There is a new fascism in Europe that has to be defeated,” he said,
“My heart goes out to family members who now live this life, but particularly those in the east of Ukraine,” he told BBC Radio Wales’ Sunday Supplement .
Residents living in parts of eastern Donetsk have been told to evacuate the area.
Mr Antoniw said there was “unity” among the Ukrainian people because “there is no alternative, there is no negotiation”.
He said: “I was in Kyiv until the day before the invasion actually started in Ukraine, I managed to meet for a couple of hours some family members of mine.
“But of course, I have others who are serving in the east, who are in the forces – we’ve lost one family member already.
“It is the day-to-day continual, repetitive information about atrocities, torture, concentration camps, liquidation squads.”
The MS, who also serves as the counsel general for Wales, has just returned from the country delivering supplies donated by trade unions.
Mr Antoniw said Ukrainian miners’ union members were asking for pick up vehicles to deliver people to the front lines.
They had delivered “an enormous amount of medical supplies”, including tourniquets and trauma bandages, he said.
“Gas supplies no longer exist in Donetsk – they will face a very very cold winter.
“Emotionally it is very difficult to see.”