The group used the Prague-based Voice of Europe news site to spread information seeking to discourage the European Union from sending aid to Ukraine, which has been battling a Russian invasion since February 2022.
Fiala said the Czech Security Information Service (BIS) discovered that the pro-Russian network was indulging in activities that "would have a serious impact on the security of the Czech Republic and the EU."
"This group sought to carry out operations and activities on EU territory aimed against the territorial integrity, sovereignty and independence of Ukraine," Fiala told reporters.
"The group's activity... also reaches the European Parliament," he said, refusing to disclose further details.
The Denik N daily said the news site had published statements by politicians demanding the EU halt aid to Ukraine.
Some European politicians cooperating with the news site were paid from Russian funds that in some cases also covered their 2024 EU election campaign, the daily adds.
The payments targeted politicians from Belgium, France, Germany, Hungary, the Netherlands and Poland, Denik N said, citing a Czech foreign ministry source.
It singled out the far-right German party Alternative for Germany (AfD) as being involved.