Melita Močnik, the head of the border police at the Ljubljana General Police Administration, told Wednesday's press conference in Rosalnice near Metlika that the pressure on the Slovenian southern border was "quite big".
Between 50,000 and 60,000 people are moving towards Slovenia from Greece and the number of illegal crossings of the border is expected to rise in the warm summer months, she noted.
She said the police may decide to call in the reserves like during last year's tourist season. If the situation escalates, Močnik said this would be "very probable".
The Slovenian police is in constant contact with the Croatian counterparts on the national and regional levels.
Preventing illegal migrations is an "absolute priority" of the Slovenian police, so if necessary, additional staff will be hired, Močnik said.
This year, just over a hundred police officers will finish education and join the police force. They will mostly work on the border.
However, in case the pressure on Slovenia's southern border rises significantly, Močnik does not exclude the possibility of seeking international assistance.
Commenting on the recent trends in illegal migration, she said that compared to the first wave of mass migrations, when mostly Syrians had entered the country, now the police were dealing mostly with people from Algeria, Morocco, Tunisia and Pakistan.
The migrants ask for asylum in almost every country they cross before moving further to the west.
In the first four months of the year, the number of persons caught crossing the land border illegally in the Koper area rose by 325% year-on-year, from 162 to 526, while the Novo Mesto Police Department recorded 509 illegal migrants so far this year, which compares to 62 in the same period last year.
Six people have drowned while trying to swim across the border river Kolpa, four have been found by Slovenian authorities and two on the Croatian side.