Image copyright AFP Image caption President Ghani vowed that the fight against corruption would be done in "a thorough and systematic way"

Afghanistan's new leader is resuming the investigation into a banking fraud said to be one of the world's largest.

Ashraf Ghani said reopening the Kabul Bank inquiry was the first step in a fight against corruption.

The bank collapsed in 2010 after losing almost $1bn (£600m), mostly deposited by international donors.

Many of the bank's staff were sent to prison but the brothers of former President Hamid Karzai, who were involved, were granted immunity.

The bank's founder, Sherkhan Farnood, and ex-CEO Khalilullah Ferozi were jailed for five years after being convicted last year of taking $810m of the $935m stolen.

Their sentence was described as "relatively light" by an anti-corruption watchdog.

Eighteen others were also jailed but Mr Karzai's brothers and one of his vice-presidents escaped prosecution because they had returned stolen funds.

'The time for action has come'

President Ghani, a former economist at the World Bank, said he was appointing a new team to look into the fraud, fulfilling pledges he made in the campaign to cut corruption.

"The time for action has come and, as we pledged, the fight against corruption will be done in a thorough and systematic way," he told reporters in Kabul.

The BBC's David Loyn in Kabul says international donors froze aid to Afghanistan when the bank collapsed four years ago.

But aid was restarted after intensive investigations carried out by donors foundered, our correspondent adds.

Most of the $935m that was lost remains undiscovered.

Mr Ghani was only sworn in as Afghanistan's new president on Monday, in the country's first democratic transfer of power.

The Kabul ceremony followed six months of bitter dispute over electoral fraud that was ended by a US-brokered unity deal that saw Mr Ghani share power with runner-up Abdullah Abdullah, who becomes chief executive.

His government's first act was to sign a security deal with US officials that will allow US troops to remain in the country beyond this year.

Kabul Bank timeline

2004: Kabul Bank founded by international poker player Sherkhan Farnood

September 2010: Kabul Bank taken over by the central bank after a run on the bank amid fears of its collapse

February 2011: Abdul Qadeer Fitrat, central bank governor, tells BBC those involved in bank's woes should be prosecuted

February 2011: An IMF report recommends the bank be put in receivership

April 2011: Mr Fitrat names in parliament prominent Afghan figures in connection with the Kabul Bank scandal

May 2011: Report by anti-corruption office shows outstanding loans worth $467m were made without appropriate collateral

June 2011: Mr Fitrat flees to the US saying his life is in danger

June 2012: Special tribunal for Kabul Bank set up by Afghanistan's Supreme Court

November 2012: Independent leaked report from Kroll auditors finds the bank funnelled almost $900m to small political elite

March 2013: Farnood and ex-CEO Khalilullah Ferozi found guilty of theft and both sentenced to five years in prison