Bulgaria detained 39 Syrians in a forest near the western town of Pernik after they were apparently abandoned on a motorway as they tried to make it from Bulgaria into neighbouring Serbia, the district governor said on Friday.

"They do not have documents," Pernik governor Irena Sokolova said. "These are people who have passed the primary interviews and procedures required for granting them refugee status.

Valentin Buchinski, the director of the district directorate of the police in Pernik, said they were Syrian.

It was not immediately clear where the interviews had taken place, or who was transporting the group that Buchinski said comprised 20 men, 14 women and five children.

On Wednesday, the Bulgarian authorities detained 125 foreigners in the capital Sofia for illegally crossing into the country without submitting an asylum request.