Hungarian PM Viktor Orban has said his Croatian counterpart is a leftist mouthpiece tasked with attacking Hungary, as a row over migrants grows.
He said Zoran Milanovic was an envoy of the Socialist International, whose members believed the current influx of migrants was “a good thing”.
Tensions between the two nations have risen since Hungary erected a barbed wire fence on the Serbian border.
This forced migrants to go to Croatia, prompting criticism from Zagreb.
Hungary completed the construction of the fence along its 175km-long (109 miles) border with Serbia in September, and is now building a similar barrier on its border with Croatia.
Thousands of migrants – many of them fleeing conflicts in the Middle East and North Africa – have been arriving in the three countries as they seek to move to wealthier EU nations.