A total of 162 people illegally residing in Bulgaria have been arrested in a specialized operation, police say.
The operation began in the morning, with dozens being detained in the first few hours.
Police referred to those sought and arrested as "foreign nationals", without specifying their country of origin.
The development comes amid fears of increased migratory pressure from Turkey, but also amid accusations from Serbia that Bulgaria's lax border controls are resulting in hundreds of Middle Eastern migrants entering the country.
Earlier, 45 people, reportedly from Iran, Afghanistan and Pakistan, were
arrested while trying to cross into Serbia.