The Ljubljana-based daily Delo carried a three-column article on the front page, describing the circumstances surrounding the arrest of Janez Podobnik and 11 members of his SLS party at the Plovanija border crossing on Wednesday, and Ljubljana's diplomatic response.
The newspaper quoted Prime Minister Anton Rop as saying that the incident would "distance Croatia from the European Union" and that Ljubljana had already notified the relevant EU institutions.
"It is an intolerable and un-European act. It is not directed only against Slovenia, but also against the European Union," Rop said.
Delo also said that under an EU decision Croatia had the duty to regulate its relations with neighbouring countries, resolve the border issue with Slovenia and the issue of "a unilaterally declared Adriatic zone" within the next year or two as part of its efforts to join the bloc.
Newspapers devoted a lot of attention to the impact of the border incident on the forthcoming parliamentary elections, scheduled for October 3.
The issue of Slovenia's access to the open sea and the issue of Istrian hamlets south of the Dragonja river have been in the focus of the election campaign and have been mainly exploited by centre-right parties, including the SLS.