The bank said the panel had not provided them details, so it was unable to verify. "The Panel’s report makes no allegation of misconduct against Salaam Somali Bank," it said in a statement. "There has also been no instance where Salaam has opened an account for a sanctioned individual or entity."

Somalia's Financial Reporting Center, which oversees compliance laws against money laundering and terror financing, said it is investigating the allegations against Salaam.

Nearly $1.7 million moved through one of the accounts during a 10-week period until mid-July this year, the report said, noting the account appeared set up to receive Islamic tax called zakat.

MULTI-MILLION TURNOVER

With around 5,000 fighters, al Shabaab controls towns and countryside in southern Somalia, but its spies and assassins operate nationwide. Its estimated expenditure last year was around $21 million, with about a quarter of that going to the Amniyat intelligence arm.

Al Shabaab also runs its own courts. One businessman told investigators that the courts had summoned him this year and ordered him to pay more than $100,000 in zakat based on a review of his business, which they had assessed before he arrived.

The businessman, who was not named, provided a banking deposit slip and a receipt from al Shabaab to investigators as proof of payment.

Another account, which appeared to handle fees levied on businessmen using Mogadishu port, had $1.1 million moved through it from mid-Febuary until the end of June this year, the report said. It included a cash deposit of $25,000 by someone calling himself "A B C" on documentation.

In total, the two accounts made more than 128 transactions exceeding the $10,000 threshold that should trigger automatic reporting to the Financial Reporting Centre.

When asked if the accounts had been shut down, Amina Ali, head of the centre, told Reuters: "All the necessary steps have been taken."

The report also examined a single road checkpoint - one of dozens - that former al Shabaab tax officials told investigators made between $1.8 million-$2.4 million per year.

In the government-controlled southern port of Kismayo, businesses are forced to pay the insurgency between $300-$600 monthly depending on their size, which could earn them nearly $6 million a year from Kismayo alone, the report said.

Businessmen are afraid to refuse al Shabaab for fear of being killed, said Hussein Sheikh Ali, a former Somali national security advisor and founder of the Mogadishu-based Hiraal Institute thinktank.

"Shabaab is super efficient in terms of collecting money throughout industries and the country," said Ali, whose thinktank's report on al Shabaab finances is due out this month.

"We know they have surplus money... and we believe they may send some money to al Qaeda."

Reporting by Michelle Nichols in New York and Katharine Houreld in Nairobi; Editing by Andrew Cawthorne