In an interview with Bild TV on Monday night, Merz said Germany is "now experiencing welfare tourism among these refugees" and accused many of them of "taking advantage of the system" by going back and forth between Germany and Ukraine.
In a tweet the day after, Merz apologized for his choice of words.
"I regret using the word 'welfare tourism.' It was an inaccurate description of a problem observed in individual cases," Merz said.
"Far be it from me to criticize refugees from Ukraine, who are facing a hard fate," he added.
Ambassador slams 'nonsense'
The outgoing Ukrainian ambassador in Berlin, Andriy Melnyk, quickly condemned Merz's characterization of war refugees.
"Where does this nonsense about alleged 'welfare tourism' of Ukrainian war refugees come from?" he wrote on Twitter.
Germany has taken in almost one million refugees from Ukraine since Russia invaded in February. These new arrivals can register to get a special status that entitles them to certain social benefits, medical care, accommodation, and access to integration courses.
Ukrainian pupils in Germany
'Absolutely out of place'
As the leader of the main conservative party in Germany, Merz's comments drew criticism from across the political spectrum.
"Using Ukrainian women and children who have fled Putin's bombs and tanks to make a political point is shameful," Interior Minister Nancy Faeser from the center-left Social Democratic Party (SPD) tweeted.
The SPD's whip in the German parliament, Katja Mast, accused Merz of imitating the far-right Alternative for Germany (AfD) party. She also called his subsequent apology "half-hearted."
The parliamentary group leader of the neoliberal Free Democrats (FDP), Christian Dürr, added that Merz's comments were "absolutely out of place."
"The people from Ukraine come to us because they're fleeing Putin's brutal war," he told the DPA news agency. "Many of them have lost everything and fear for their loved ones."
zc/dj (dpa, AFP)
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