Barclays has not revealed which payments between it and Qatar are being investigated by the SFO.
The bank raised some £2bn from Qatar Holding in 2008.
Funds raised from investors in Qatar and Abu Dhabi that year allowed Barclays to avoid being semi-nationalised along with Royal Bank of Scotland and Lloyds.
In July, the Financial Services Authority said it was investigating both the bank and four current and former senior employees, including finance director Chris Lucas.
Barclays recently faced an USD 450m find for rigging the Libor rate, resulting in stepping down of the bank’s Chief Executive, Bob Diamond, and Bank chairman Marcus Agius.