The visiting fans twice halted play, tossing flares onto the San Siro pitch and later clashed with the police. Croatian media reported that 17 fans were arrested.
"These hooligans have shocked soccer-loving Europe and deserve nothing but condemnation of the entire society. We call upon the Croatian judiciary to process all those who took part in the incident," HNS said in a statement entitled 'Let's put an end to hooliganism' and posted on their website.
"We also urge the other segments of the Croatian society, starting with the government, to see those incidents as the last straw, which will prompt all those in power to an energetic and decisive action," it said.
Croatian fans have a history of unruly behaviour ranging from racism and fascist chants to flare-throwing and clashes with the police.
"Such incidents are obviously the result of the failure to act earlier. They are a shame for the Croatian state and have resulted in unforeseeable consequences for Croatian soccer and the national team," the HNS statement said.
(Reporting by Zoran Radosavljevic; editing by Justin Palmer)
