Some foreigners who fled their countries with criminal records and entered the country are security threats to nationals.
Juba University lecturer Venansio Tombe Muludiang told the press on Thursday that many foreigners enter the country without legal documents and are never properly scrutinized at the borders.
He cautioned that some immigrants are illegally residing in South Sudan causing insecurity.
Professor Muludiang said currently rural-urban migration cannot be controlled because many people move according to their will as guaranteed by the constitution.
He said some people move to towns before securing jobs.
Professor Muludiang comment marked the International Youth Day.