South African police say they are investigating whether more than $5 million seized from five passengers bound for Dubai in August was part of a fundraising scheme by Islamic extremists.

Police Brig. Hangwani Mulaudzi said Tuesday that there were "rumors" that the cash was headed for the Islamic State group but that authorities had so far not found any "tangible evidence."

Islamic State extremists control parts of Syria and Iraq and have welcomed thousands of foreign fighters into their ranks.

South African tax authorities say five passengers carrying the cash were detained while boarded an Emirates flight at Johannesburg's main international airport on Aug. 28.

Authorities say the cash, packed in 11 bags, was delivered to the South African Reserve Bank for investigation.