The vehicle, a taxi with Latvian registration numbers, was driven by a Latvian citizen, 58, with all necessary personal and car documents.
The border guards, however, paid attention to the five passengers. It turned out that the man, 34, and the woman, 24, both Russian citizens, had only Latvia-issued asylum seekers' documents that do not give the right to foreigners to leave the country.
Three minors were also travelling with the couple.
A pre-trial investigation has been launched against the Latvian citizen for illegal cross-border transportation of people.
A decision on the detained foreigners' extradition to the neighboring country is expected later in the day.