Mai Ahmad Fatty said financial experts were trying to evaluate the exact loss.

Luxury cars and other items were reportedly loaded on to a Chadian cargo plane as Mr Jammeh left the country.

Mr Jammeh, who flew into exile after 22 years in power, has not commented on the allegations.

He had refused to accept election results but finally left after mediation by regional leaders and the threat of military intervention.

President Barrow remains in neighbouring Senegal and it is not clear when he will return.

However, West African troops entered the Gambian capital, Banjul, on Sunday to prepare for his arrival.

Cheering crowds gathered outside the State House to watch soldiers secure the building.

The Senegalese general leading the joint force from five African nations said they were controlling "strategic points to ensure the safety of the population and facilitate... Mr Barrow's assumption of his role".

Is $11m a lot for The Gambia?

Mr Fatty told reporters in the Senegalese capital Dakar that The Gambia was in financial distress.

"The coffers are virtually empty," he said. "It has been confirmed by technicians in the ministry of finance and the Central Bank of the Gambia."

He said Mr Jammeh had made off with nearly 500 million dalasis ($11.3m) in the past two weeks alone.

"That's a lot of money, considering that we spend about 200 million dalasis on required expenditure relating to payment of civil service and so forth," Mr Fatty told the BBC.

Mr Fatty said officials at The Gambia's main airport had been told not to let any of Mr Jammeh's belongings leave the country.

However, two Rolls-Royces and a Bentley were flown out over the weekend, and 10 others were at the airport waiting to go, reports the BBC's Umaru Fofana from Banjul.

Reports said some of the former leader's goods were in Guinea where Mr Jammeh had stopped on his journey into exile.

So where is Mr Jammeh now?

Mr Jammeh is reported to now be in Equatorial Guinea, although authorities there have not confirmed it.

He is suspected to have business interests in the oil-rich state, and is likely to be protected by President Teodoro Obiang Nguema.

The president has ruled the central African country since 1979, and is seen to be authoritarian, like Mr Jammeh.

Equatorial Guinea does not recognise the International Criminal Court (ICC) and has weak civil society and opposition groups, reducing the chances of the government coming under pressure to hand over Mr Jammeh to either the ICC or Mr Barrow's government for prosecution.

But could he be pursued?

The UN, African Union (AU) and Economic Community of West African States (Ecowas) had issued a joint statement, promising to protect Mr Jammeh's rights "as a citizen, a party leader and a former Head of State".

They also gave an assurance that his "lawful" assets would not be seized.

However, Mr Fatty distanced Mr Barrow from the undertaking.

"As far as we're concerned, it doesn't exist,'' he was quoted by the Associated Press news agency as saying.