The central bank of Tanzania has said that the closure of forex exchange (forex) bureaus in the northern city of Arusha comes as a result of a six-month investigation into businesses that had been operating illegally.

It found an increase in businesses operating without a licence, and some involving money laundering, the bank's governor, Florens Luoga, said in a statement.

Mr Luoga said the country's various investigative units took part in an a coordinated operation.

Army officers had been involved in the raids because a majority of the police force had been providing security at schools during the examination period, he said.

Those found to have broken the law would be prosecuted and their licences revoked - if they had them, the central bank governor said.

He added that no new licences would be given to operate forex bureaus until new rules to regulate the money exchange shops were agreed.

Meanwhile, tourists and tour firms have been struggling to change money in Arusha as the forex shops remain closed.

The town is a gateway for those visiting Mount Kilimanjaro and the Serengeti national park.